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N1J J INSTITUTE OF SCIENCE AND TECHNOLOGY THE UNIVERSITY 01' MIClflGAN POST OFFICE BOX (, IH ANN ARBOR, MICHIGAN 4H107 Telephone 313· 4H3 ·0500 '''Made avallabre under NASA sponsOrsl1'~ in the interest of early and wide dis- . seminatio,n of Earth,Resources Sur-vey' Program Information and without liability for any use made thereof." October 31, 1972 11229-l0-L ~\ E72-101.98. . t"R_ IJ90~1(\ . National Aeronautics and Space Administration Goddard Space Flight Center Greenbelt Road Greenbelt, Maryland 20771 Attention: Mr. E•.F. Szajna, Code 430 Contract: NASS-2l783 Subject: Second Bimonthly Report For Period Covering 1 September-3l October, 1972. Dear Sir; The enclosed material comprises the second Type I bimonthly technical report for contract NASS-2l783, and reports progress on the ten tasks of this program for the period 1 September-3l October, 1972. Financial reports 533M and 533Q are submitted separately from our Accounting Department. Work on this contract is performed in the Infrared and Optics Division (Tasks 1-3 and 5-10)directed by Mr. Richard Legault and in the Radar and Optics Division (Task 4) directed by Dr. Leonard Porcello. Principal Investigators for each task are listed on the report subsections associated with those tasks. Three important aspects of the effort at Michigan deserve general discussion. First, a prototype computer based data management system is now running on the IBM 360 computer on campus to catalog digital magnetic tapes. All pertinent data about the tapes is stored for automatic retrieval. By use of an editing retrieval program, only data of interest to the investigator may be listed on page printer or time sharing station teletype. In addition to editing searches, plans are to publish periodic lists of additions to the system. Second, ERTS-l CCT's of the San Francisco frame (1003-18175) were success- fully processed tothe color coded recognition map stage. This was done to assess the state of readiness of the IBM-7094 software system. Problems identified in this simulation run on real ERTS-l data are now being addressed by . - ---- ---- ~ - - ------ - ---- - - ~ - -- ----- ._-------- iE72-101~8) (ERTS COMPUTER COMPATIBLE TAPE DATA PROCESSING AND ANALYSIS. APPENDIX 1: .THE UTILITY OF IMAGING RADARS FOR THE STUDY ~OF LAKE ICE) F.C. Polcyn, et al (Michigan Unlv.) 31 Oct. 1972 30 P CSCL 08H G3/13 N73-11296 Unclas 00198 INSTITUTE OF SCIENCE AND TECHNOLOGY THE UNIVERSITY OF MICHIGAN Page Two l1229-l0-L programmers. Because the processed results from the Sacramento Valley have the potential of being significant results, some effort has been expended checking the recognition map in the field. Based on Mr. Sadowski's field trip to the site, a modifie4 set of spectral signatures, each signature representing a particular crop type, has been suggested. A second recognition map will be prepared. Analysis of this map should yield useful results in determining the ability to map important crops ,from ERTS-l data and determine their acreages. Third, it is clear that the length of the first look data phase will be longer than the three months originally anticipated. This extension is caused by the fact that magnetic tapes ordered from Goddard have not yet arrived. Investigators for tasks II, VI, VII, VIII, and X have ordered magnetic tapes but only Wezernak (Task VIII) has obtained tapes to date. Investigators for tasks I, III, IV, V, and IX have not yet received any imagery. For tasks III, V, and IX cloudy sky conditions have precluded obtaining any useful imagery. Task IV deals with lake ice and the standing order is not in force as yet. Task I has not received data apparently becaused of tape recorder priorities in the collection of data over Puerto Rico. The Lake Michigan site for task I has been covered, but no imagery has been received to date. Data from the first two orbital cycles are Y~own to be unusable because of 100% cloud cover but status of data from the next 3 orbital cycles is unknown at present. Table I shows the tasks presently being pursued under contract NAS5-2l783. Reports by individual investigators follow in order of task number. Respectfully submitted J:-;) (\,- \ 01\ \ r-\l "lJ2.:~cc. ,\;I~ -J I LL-t5YvL-L~ Frederick J. Thomson Associate Research Engineer J2 1'') (t~'L ~ ., fe' c< . R. R. Legault Associate Director- -Willow Run Laboratories FJT:RRL:cmk 11229-10-L Pag~ Three ERTS PROGRAM SUMMARY Under Contract NAS5-21783 PRINCIPAL TASK INVESTIGATOR MMC /I UN SHORT TITLE I Polcyn 063 200 Water Depth Measurement II Thomson 077 621 Yellowstone Park Data III Thomson 137 636 Atmospheric Effects (Colorado) IV Porcello 072 201 Lake Ice Surveillance V Sattinger 086 225 Recreational Land Use VI Polcyn 114 635 IFYGL (Lake Ontario) VII Mali1a/ 136 612 Image Enhancement Nalepka 178 VIII . Wezernak 081 625 Water Quality Monitoring IX Horvath 079 606 Oil Pollution Detection X Vincent 075 422 Mapping Iron Compounds 3 11229-10-L Page I-I Second Type I Progress Report - 1 September - 31 October 1972 Task I - Water Depth Measurements - 1388 F. Polcyn, UN 200 Since no data had been received, a request was made of the User Services at NASA Goddard for any data collected in the Virgin Islands. It was found that data over this test site must be tape recorded and data from only one pass . was recorded. A request for any 'frames available was made and is pending. Data over While there has been received. researcher over lies in a small the second test site in Upper Lake Michigan is also missing. been data collected in lower parts of Lake Michigan no data has There appears to be some confusion in that useful data for one his designated site is being sent to other researchers whose area geographical part of the frame. Standing orders will be changed to extend the period of time designated for which useful space data can be collected at each test site because of season conditions. Meanwhile work continues on completing the programming effort for using water depth subroutines on 'the 7094 computer. 11229-l0-L Page 11-1 Second Type I Progress Report - 1 September-3l October 1972 Task II - Yellowstone National Park Data - 1398 F. Thomson, UN 621 Since the first bimonthly report, a number of excellent ERTS-l frames have been received of the Yellowstone National Park area. These frames are summarized below and imagery content forms are attached. On 16 October, digital 7 track, 800 bpi tapes were ordered for frame 1015-17404 collected on 7 August. This frame covers the entire park, has less than 10% cloud cover, and essential park features are well portrayed. When the tapes are received and preliminarily processed, we should be able to prepare a data analysis plan. Harry Smedes concurs in the selection of the 7 August data for preliminary processing. Training sets for the recognition are now being summarized on maps. Processing is now planned for about 15 December. This starting date is based on the typically 2 month (from order date) delivery time for digital tape products. If digital tapes arrive sooner, processing will begin sooner. A considerable amount.of time has been spent getting software in shape for processing the data. Based on our experience with the San Francisco frame, some modifications were made in a tape copy program. 5 Table I-I SUMMARY OF YELLOWSTONE DATA RECEIVED TO DATE 11229-l0-L Page II-2 Frame No. . Date ·CeIitetLaL .& Ldng. Area 1014-17350 Aug 6 N 44 0 34' LAT East Edge Yellowstone W109 0 10' LONG Cody, Wyo. Black streaks in HSS-5. 1015-17404 Aug 7 N 44 0 48' LAT Yellowstone, W110 0 35' LONG Henry's Lake, Ida. 1015-17410 Aug 7 N 43 0 22' LAT Jackson Lake, W111 0 08' LONG Grand Tetons, Snake River Valley 1032-17350 Aug 24 N 45 0 06' LAT N. E. Corner Yellowstone, W108 0 54' LONG Cody, Wyo, Hontana 30% cloud cover Band MSS-7 missing '. --' N 44 0 33' 1050-17351 Sept 11 LAT East Edge Yellowstone W109 0 05' LONG Cody, Wyo. 10% cloud cover ERTS IMAGE DESCRIPTOR FORM (See Instructions on Back) DATE _...:1..:..1/:....:2:.,:./...:.7..:..2 _ PRINCIPAL INVESTIGATOR F_,_T_h_o_m_s_·o_n _ GSFC _-:UN:...:-_6_21 _ University of Michigan ORGANIZATION --.::.- ~ _ PRODUCT 10 FREQUENTLY USED DESCRIPTORS· (INCLUDE BAND AND PRODUCT) Geology Forest Agricul t~re 11229-10-L Page II-3 NDPF USE ONLY 0 _ N _ 10 _ DESCRIPTORS lOl4-l73S0M lOlS-17404M l01S-l74l0M l032-l73S0M lOSO-173S1M -I x x x x x x x x x x x x x x Rangeland, Snow Rangeland, Snow Rangeland, Snow "FOR DESCRIPTORS WHICH WILL OCCUR FREQUENTLY, WRITE THE DESCRIPTOR TERMS IN THESE COLUMN HEADING SPACES NOW AND USE A CHECK (J) MARK IN THE APPROPRIATE PRODUCT 10 LINES. (FOR OTHER DESCRIPTORS, WRITE THE TERM UNDER THE DESCRIPTORS COLUMN). MAIL TO ERTS USER SERVICES ':. CODE 563 BLDG 23 ROOM E413 NASA GSFC GREENBELT, MD. 20771 301-982-5406 GSFC 37-2 (7/72) 11229-10-L Page 111-1 Second Type I Progress Report - 1 September - 31 October 1972 Task III - Atmospheric Effects in ERTS-1 Data - 1410 F. Thomson, UN 636 No acceptable ERTS-l data was obtained in the overpass of 9/6/72 and no, data are listed in the September 30 catalog for the overpass of 9/7/72. Roland Hulstrom of Martin - Marietta made atmospheric measurements in the test site in this time frame. Had we obtained good ERTS data on this pass we probably could have conducted'an assessment of the atmospheric effects and have written a data analysis plan. A frame of data was ordered from the 25 S,eptember overpass. While this data is outside the range of the initial standing order, the frame was ordered to provide an introductory look at the test site. Because snow now covers the test site, data collected from now until April 1973 will probably have limited utility to implementing the experiment as now planned. Thoughts will be crystallized in the next bimonthly period on possible alternative plans which will allow the experiment objectives to be fulfilled with alternative data sets. These plans will then be discussed with the scientific and technical monitors. 11229-l0-L Task IV-l Second Type I Progress Report - 1 September - 31 October 1972 Task IV - Lake Ice Surveillance -1406 L. Porcello, UN 201 The only problem which has arisen during this second two month period is the long delivery time for a few components of the instrument discussed in the 31 August 1972 Type 1 bimonthly report. Plans are continuing to prepare for the aircraft underflights and ground truth operations during the ERTS-l passes. It is tentatively planned to conduct these "earth based" portions of the project on 15 January 1973, 10 March 1973 and 15 April 1973, although these times are flexible as may be required by the conditions at the time. Flight and ground operations may be off by a day or two, but they must remain to be simultaneous with one another. The flight lines have been tentatively identified to cover Douglas Lake and mlitefish Bay at the entrance of the St. Mary's River and the Straits area of Lake Michigan. It is noted that the number of flights has been reduced from 6 to 3. This reduction will not seriously hamper the study although it may reduce the variations in ice types which will be studied d~ring the field period. Initial efforts are being 'conducted to contact individuals and agencies which are presently involved in ice studies and reports on the Great Lakes. It is intended to try to coordinate their mesoscale reports with hour proposed microscale ground truth and the macroscale ERTS-l imagery. This should cause no change in the program as written through the ERTS-l contract, but should i~crease the amount of ground truth data to be correlated with the ERTS-l imagery and thus increase the scope of ERTS imagery usefulness. At this time, no "significant results" have been realized. One paper: "The Utility of Imaging Radars for the Study of Lake Ice" was presented at the International Symposia on the Role of Snow and Ice in Hydrology held in September at Banff, Alberta, Canada. A xerox copy of the preprint of this paper is enclosed as Appendix I. A corrected version will . be published in the. Proceedings of the Symposia. Multiple copies of this paper are presently available. This report was generated on funds provided by the Director of Willow Run Laboratories. The information copy of the report is attached and is being sent to NTIS because of its pertinence to the Task IV ERTS-l investigation. Order forms for both test sites, submitted on 13 December 1971 under user ID UN 201, Proposal #MMC-072 show (p. 4 of 5) that we requested 1 copy Bulk B&W 70mm (ng. transparency) RBV (1, 2, 3) and MSS (4, 5, 6, 7), 4 copies Bulk B&W 9.5" Positive Paper Print (RBV 1, 2, 3) and HSS (4, 5, 6, 7) and 2 copies Precision B&W 4.5" Pos. Paper Print (RBV, 1, 2, 3) and MSS(4, 5, 6, 7) for each site. It was also indicated that we did not intend to order for all cycles marked on Section 3.2 of that form. We now wish to change that request to have the above enumerated products delivered for all cycle which passes over the test sites as outlined on the ERTS-l Product Order Forms. 11229-l0-L Page V-I Second Type I Progress Report - 1 September 1972 - 31 October 1972 Task V - Recreational Land Use - 1387 I. Sattinger, UN 225 Photographic results of RB57 Mission 205 flown over Southeast Michigan (Site 279) in June 1972 were received during September. Preliminary examination of the photography shows that coverage of parts of Oakland County was obtained, 'but that other parts could not be photographed due to developing cloud cover. However, coverage of other parts of Southeast .Michigan was obtained which will be useful for some aspects of the investigation. It is understood that an attempt was made during Mission 211 in September to obtain additional coverage of the area, but this was again prevented by cloud cover. In the absence of complete coverage of Oakland County, the RB57 photography will be used as much as possible and supplemented where necessary by previous coverage obtained in 1969. If it appears by next spring that additional photography is needed to . complete the work, a new request will be submitted at that time. Full-scale analysis for this task must await receipt of ERTS-l imagery for Southeast Michigan. At the end of this reporting period, no useful coverage of the test area had yet been obtained. However, preliminary study of RB57 photq.grepl:!y and C47 .scanner imagery is being conducted in preparation for the analysis of satellite data. The useful RBS7 imagery of Oakland County and 9 in. x 9 in. color infrared imagery of the C47 test site taken during the C47 flight is being examined to determine the types of vegetation, water bodies, and residential areas to be identified in the ERTS-l data. A portion of the C47 scanner data acqUired during the August 29 flight is being processed. This portion covers a part of the Pointe Mouillee State Game Area at the mouth of the Huron River. Studies of this waterfowl habitat area being conducted under other projects will provide useful ground truth data on vegetation species for verification purposes when ERTS data becomes available. During the next reporting period, study of RBS7 photography and C47 scanner imagery will be continued for the purpose of further defining the plan for analyzing ERTS-l data when it becomes available. /0 ll229-l0-L Page VI-l Second Type I Progress Report - 1 September - 31 October 1972 Task VI - IFYGL (Lake Ontario) - 1384 F. Polcyn, UN 635 MSS images of the western and eastern ends of the Lake Ontario Basin were received during this period.. These frames were recorded on August 19 and 21 and appear to be of good quality. Unfortunately ERTS imagery of the central portion of Lake Ontario was not collected by ERTS at that time. These frames are being considered for automatic processing using multispectral discrimination techniques. . Two attempts were made to obtain supporting U of M aircraft data at times of ERTS passes -- September 8th and October 13-l4th. The September mission was aborted due to technical aircraft problems after two f1ight1ines had been flown and poor weather conditions during the October mission prevented any aircraft data collection on that date. Current plans include 1) continued attempts to obtain supporting airc~aft data, 2) obtaining ERTS imagery from passes over the Lake Ontario Basin subse~uen~ to the mid-August pass, and 3) continued coordination of ground observation efforts with various IFYGL cooperating universities and agencies. It is unfortunate that to date weather conditions have been generally unseasonably poor during times of ERTS passes over the Lake Ontario Basin. fI 11229-l0-L Page VII-l Second Type I Progress Report - 1 September-3l October 1972 Task VII - Image Enhancement - 1385 W. Malila, UN 612, and R. Nalepka, UN 178 Experience has been gained at WRL over the past decade in computer processing and extraction of information from airborne multispectral scanner data and in modeling atmospheric effects in received radiance signals. The general objective of Task VII is to adapt techniques. existing at WRL for their application to ERTS-l data, to assess the applicability of these techniques by applying them to selected ERTS-l data, and to identify any additional problems that might be associated with such processing of satellite multispectral scanner data. Three areas are to be studied: (1) compensation for atmospheric effects in ERTS-l data, (2) preprocessing for improved recognition performance, and (3) estimation of proportions of unresolved objects in individual resolution elements. The principal activities prior to and during the current reporting period have been in planning data collection activities, providing ground support for aircraft and ERTS-l overflights, making field observations in the test site area, and modifying computer software to handle ERTS data. . The intensive test site for this investigation is an agricultural area South-loJest of Lansing, Michigan, and the extensive test area also covers several other counties in South Central Michigan. Field data on the identity of crops planted in a large fraction of the fields in the extensive test area had been obtained through the cooperation of ASCS personnel of the USDA and coordination efforts of Michigan State University (MSU) personnel, although only data for the intensive area are presently at our disposal. In addition, extensive field checking and ground photography were carried out in the intensive test area by MSU personnel with assistance from WRL personnel. RB-57 camera coverage of the region was obtained during June, but was not available for use in this effort. The intensive test area is in an overlap region covered by ERTS-l on two successive days of each l8-day cycle. On 6, 7, and 24 August, there were heavy cloud overcasts, but skies were clear on 25 August. Simultaneous multi-altitude underflight coverage was obtained by the Michigan c-47 multispectral scanner .... aircraft, and ground-based measurements were made of spectral irradiance and sky radiance. No ERTS imagery was received prior to the current reporting period. Imagery from the Aug. 25th pass over our test site was received on Oct. 18th. A preliminary analysis showed it to be cloud-free over the intensive test area 'and a majority of the remainder of the frame. Thus, it will serve as a major data base for the investigation. Computer-compatible tapes were ordered immediately for our analyses. Color-composite images also were ordered from ERTS User Services. A phone call was made to the Aircraft Program Office at the Manned Spacecraft Center, Houston, Texas, to confirm our immediate need for copies of photographs and imagery collected by the Michigan multispectral scanner aircraft. RB-57 photography from June 10/11 was received on Sept. 22nd. A second RB-57 flight was made on Sept. 15th and copies of the photographs were received Oct. 27th. ('I- l1229-l0-L Page VII-2 Field observation data along a 10-mile segment of the test site were consolidated and preparations begun for analysis of the scanner data. Visual range measurements at 10:00, 11:00, and 12:00 (noon) on Aug. 25th were collected for all reporting weather stations in the ERTS frame. In addition to that from Aug. 25th, imagery was received from Aug. 6, 7, 8, and 24 and Sept. 9, 11, 12, and 13. Most of these suffered from cloud cover in the test area. Image descriptor forms were forwarded for nine frames. The planned aircraft underflights on S~pt. 11 and 12 were cancelled because of weather conditions. Dr. Robert Fraser, GSFC, visited liRL on Oct. 19th to discuss plans and progress on the atmospheric portions of our study. Plans for the next reporting period are to plan and begin analyses of ERTS-l CCT data and supporting aircraft multispectral scanner data for the Aug. 25th frame. /3 l1229-l0-L Page VIII-l Second Type I Progress Report - 1 September - 31 October 1972 Task VIII - Water Quality Monitoring - 1400 C. T. Wezernak, UN 625 Work during the reporting period consisted of: 1. Examination of available satellite imagery (70 rom positives and negatives) for the test sites included in this investigation 2. Review of available aircraft imagery 3. Preliminary analysis of satellite and aircraft data 4. Preparation of a plan for preliminary data analysis. During the reporting period, data became available for the New York Bight. A preliminary analysis was made and results were reported at the ERTS seminar "Preliminary Findings From Analyses of ERTS Observations" held at Goddard on 29 September 1972. Digital tapes for the study area have been received and the data will be preliminary processed during the next reporting period. Product order requests have been submitted for the other test sites. Data will be processed as it becomes available. During the next reporting period, multispectral aircraft missions in support-Of-the program have been authorized for the New York, S. E. Florida, and Tampa study areas. Accordingly, ground truth activities in support of these missions are planned. The following talks and publications have been released during the reporting period: 1. "Barge Dumping of Wastes in the New York Bight" presented at Goddard ERTS seminar on September 29, 1972, Report No. 011229-6-S, NASA-CR 128099, E72-l0084. 2. "Remote Sensing in the New York Bight", presented at the New York Bight Conference held at NOAA, Rockville, Maryland, on 12 September 1972. This was a meeting of government agencies which have programs in the New York Bight area. The ERTS program for the area was described-and examples of aircraft data were shown. The ERTS Image Descriptor Form which relates to the New York Bight analysis is attached. The standard vocabulary of image descriptors was used, except that the term pollution was added. In general this vocabulary is inadequate to describe image content. The following Data Request Forms have been submitted: 1. New York Bight 14 September 1972 2. Tampa Bay 6 October 1972 3. Lake Michigan 11 October 1972 4. Santa Barbara Channel 12 October 1972 5. Lake Erie 17 October 1972 These include requests for imagery and digital tapes. To date, only digital tapes for the New York test site have been received. 14 ERTS IMAGE DESCRIPTOR FORM (See Instructions on Back) DATE ---.:1:.....-N_o_v_e_m_b_e_r_1_9_7_2 _ C.T. Wezernak PRINCIPAL INVESTIGATOR _ GSFC __U_N_6_25 _ Willow Run Lab. ORGANIZATION _ PRODUCT 10 FREQUENTLY USED DESCRIPTORS· (INCLUDE BAND AND PRODUCT) 11229-10-L Page VIII-2 NDPF USE ONLY D ~_ N _ 10 _ DESCRIPTORS 1024150714} 1024150715 1024150716 . 102415071M Oceanography, river, sediment, slick, pollution, current Estuary, Coastline Harbor *FOR DESCRIPTORS WHICH WILL OCCUR FREQUENTLY, WRITE THE DESCRIPTOR TERMS IN THESE COLUMN HEADING SPACES NOW AND USE A CHECK (J) MARK IN THE APPROPRIATE PRODUCT 10 LINES. (FOR OTHER DESCRIPTORS, WRITE THE TERM UNDER THE DESCRIPTORS COLUMN). GSFC 37-2 (7/72) MAIL TO IS ERTS USER SERVICES CODE 563 BLDG 23 ROOM E413 NASA GSFC GREENBELT, MD. 20771 301-982-5406 11229-l0-L Pag~ IX-l Second Type I Progress Report - 1 September - 31 October 1972 Task IX - Oil Pollution Detection - 1389 R. Horvath, UN 606 Work during the reporting period consisted primarily of finally establishing the total geographic scope of the program which involves complementary funding by NASA (this contract) and the U.S. Coast Guard (Contract DOT-CG-24063-A). In addition to the Chesapeake Bay test area defined in the NASA contract, U. S. Coast Guard interest has defined additional sites in the Gulf of Mexico southwest of New Orleans and in Santa Barbara Channel. These latter two areas "represent concentrations of offshore oil drilling activities as well as shipping lanes, and thus complement the shipping and shoreline industrial nature of the southern reaches of Chesapeake Bay. The Gulf of Mexico site is coincident with an ecological test site being extensively investigated by Gulf Universities Research Consortium (G.U.R.C.). Mr. C. Catoe, U.S. Coast Guard Co-investi- gator (OT30l) has arranged for access to ground truth data from the. G.U.R.C. area. No satellite data have been received to date. "A revised ERTSI "Standing Order Form was submitted on 30 October 1972. This revision added the Gulf of Mexico and Santa Barbara channel sites, and extended the time period of interest for the Chesapeake Bay site. _ t 11229-10-L Page X-I Second Type I Progress Report-l September through 31 October 1972 Task X- An ERTS Experiment for Mapping Iron Compounds - 1383 R. Vincent, UN422 During this reporting period a method for producing ratio images from ERTS data was defined, a paper concerning the experimental plan for this investigation was submitted for publication, computer programs were begun, and an ERTS frame over the Wind River test site was selected for quantitative examination. The experimental plan presented here is more fully described in a paper submitted this month to the Eighth Remote Sensing Symposium Pro- ceedings entitled "An ERTS Multispectral Scanner Experiment for Mapping Iron Compounds," by R. K. Vincent. The spectral radiance of Lambertian targets measured by ERTS MSS scanner can be expressed as = (1) - measured spectral radiance, shadow or illumination factor (1.0 for no shadow in instantaneous field of view), E = spectral irradiance of the sun (impinging upon target), sunA TA = atmospheric transmittance, PA = spectral reflectance of target, L = path radiance (caused by atmospheric scattering). PA The LPA term contains path radiance from two sources: light scattered into the beam between target and detector, and light scattered off the sun-target direction (diffuse illumination), then reflected off the target toward the detector. Whenever the LPA term is negligible, as with low-altitude scanner data on a clear day, all of the environmental factors are multiplicative~ From satellite altitudes, however, LPA is no longer negligible. To get rid of most or all of this additive term, the purely empirical approach of dark object subtraction can be taken. In a shadowed region, S = a because there is no direct solar irradiance; hence LA = LPA whenever the shadow is large compared with a spatial resolution element. Therefore, for a given spectral channel, the value of the lowest radiance measured within the scene will be subtracted from all other spatial resolution elements in the scene. After dark object subtraction, the ratio of the i th and (i + l)th channels will be approximately If 11229-10-1 Page X-2 . L S EsuniJ E [P::1] 1T TiP i suni Ti i (2) Ri,i+l %-- = SrB~ni+1 = Li +l E T suni +l i+l Ti+lP i +l In this equation, the only term which will vary widely over an ERTS frame (for most geological test sites) is Pi/Pi+l' the target reflectance term. The ratio may not be invarient for a given type of target type in two ERTS frames collected at different times indifferent places, however. For a further suppression of environmental factors (S, Esuno, Ti' and LPi) , the spectral reflectance of a known target within the ERTS frame can be measured and used as a reference, for which the ERTS-measured ratio will be: (Ri i+1) = , reference [ Pi] Pi +l .reference (3) A division of equation 2 by equation 3 yields, after rearrangement, = [P::l] reference [ Ri,i+l ] (Ri i+l) , reference (4) from which the term Pi/Pi+l can be calculated almost independent of environ- mental factors. The "almost" is included in the foregoing statement because the degree of environmental independence is dependent on how well the dark object subtraction succeeds in suppressing the path-radiance term. It should be noted that the dark object subtraction is an approximation, because part of the LPA term is dependent on target reflectance. However, it is assumed here that the target reflectance dependence of LPA is negligible. Should the above procedure yield poor results, i.e., fail to suppress . atmospheric effects, another approach will be attempted. The dark object subtraction method cannot be used to yield data from the darkest elements in the scene, however. These elements will be processed in a different manner, possibly as a straight radiance ratio. Finally ,dark object subtraction and ratio programs were begun and ERTS frame No. 1013-17294 (collected by ERTS on 5 August 1972) was selected for quantitative analysis. Tapes and images were ordered for this frame. 369430-11S-S/SA Appendix I SESSION: THE UTILITY OF IMAGING RADARS FOR THE STUDY OF LAKE ICE by M.L. Bryan WHO - 4: Measurement and Forecasting Specific to River and Lake Ice International Symposia on the Role of S110LJ and Ice in Hydrology . WMO-4 , " \. .(. !, I ,- I'j. ti,. ~i /' I'. I 1-· ;: t' I Ii.f Symposium on Meaeurement and FOl'ecaeting I$,),..~ 1111.), Sy 1z. TIlE UIILITY OF IMAGING RADARS FOR THE STUDY OF LAKE ICE by M. Leonard. Bryan SlJMl.IARY Although several remote sensing systems are available for the surveil- lance of ice and snow (e.g. aerial photography, multispectral scanners, ~~ather and earth resources satellites), they suffer from their present r~striction to the visible and infrared portions of the electromagnetic spectrum. Sidelooking airborne radar (SLAR) is not so limited. After a brief introduction to radar systems, the argument proceeds to define system ~nd ground parameters which affect the radar signal return. Two of these, dielectric constant and surface roughness,are seen to be the ~ost important with respect to the final radar image. It is noted that although SLAR has been used for surveillance of sea ice in the higher latitudes, its usefulness for the study of fresh water lake ice in the mid-latitudes is only now being intensively studied. Two images of X-Band (3 cm) radar are presented, together with some comments concerning future deve19pments of radar imagery of lake ice. L' UIILlTE DE RADARS lMAGANTS POUR L' ETUDE DE LA GLACE SUR LES LACS RESUME .. ; Malgr~ la disponibilit~ de plusieurs syst~es sensitifs de controle a distance pour la surveillance des glaces at des neiges (e.g. photographie aerienne, scrutateurs multispectrales, sat~llites de resources terrestres et de conditions atmospheriques) ceux-ci souffrent tous presentement de leurs restrictions aux portions visibles et infra-rouges du spectrum electromagnetique. Le radar oblique aeroporte (SLAR) n'est pas aussilimite. Faisant suite a une breve.presentation awe systemes de radar, l'argu- ment procede a definir les parametres de systeme et terrestre qui influencent Ie retour des signaux de radar. Deux de ceux-ci,. Ie aielectrique constant et la rugosite sur la surface sont juges les plus importants en ce qui concerne l'image finale de radar. On note aussi que malgre l'emploi deSLAR pour la surveillance de la glace oceanique awe hautes latitudes,· son utilite pour l'etude de la glace sur les lacs d'eau fraiche awe mi-latitudes, n'a jamais ete etudie serieusement jusqu'a present. Deux images de X-Band (3 cm) sont presentees, avec commentaires touchant aux developements futurs d'imageries de radar sur la glace des lacs. 2 ll\TRODUCTION: In any of the earth sciences, a major problem is the collection of meaningful synoptic and real time data, Not only must the data often be quickly available but it must also be accurate and reliable, for, when dealing with a dynamic system (e.g. climate, hydrQlogy, and to a lesser degree, glaciers, soils and sea or lake lee) we often do not have the opportunity " to repeat our measurements. If that opportunity does arise, we are con- fronted with the problem of making assumptions concerning the rate of change of the items being investigated. In addition to these difficult hurdles, we also must recognize that many of the important aspects of hydrologic studies, both in the frozen and the liquid states of water, are in relatively inaccessible regions where both intense and continuous research programmes are difficult and expensive. The Great Lakes are such an area. Fi~ally, much of the data we collect is point specific when indeed we are attempting to secure area data by summing the numerous points. As has often been observed: "Confronted by a situation as complex as the environ- ment ••• we are likely ••• to attempt to reduce it in our minds to a set of separate, simple events, in the hope that their sum will somehow picture the whole." [1] USE OF AIRCRAFT AND EARTH SATELLITES: In some early, but recent attempts at approaching this problem of areal 'coverage 'using remote sensors, cameras were mounted in airplanes and flown over the ice/snow fields in question. This method has proven to be fairly useful both for defining the extent of the snowfield and also for determining the volume of the snowpack and glaciers, especially when a series of . sequential photographs can be.made to determine the changes in the snowpack mass. [2] However, in areas where there is little shadow, it is very difficult to contour the photograph in one of the early steps in the pro- duction of a contour map for mass balance studies. " The problem is not insurmountable, but the data retrieved through such a system are limited, primarily to the areal extent of the snow and aYso by the fact that only small areas could be covered in a given time. One solution was to change the focal length of the camera or, conversely, place the camera at a higher altitude. Ultimately, this led to the" installation of cameras in earth satellites, and several (NIMBUS, TIROS, ITOS AND ERTS [A]) have been, or in the case of ERTS (A) will be used to produce excellent pictures of snow and ice covered regions of the world. Several published articles [3,4,5,6,7] have excellent examples of the imagery from such systems. One of the major problems confronting these systems which deal with the visible and near-visib"le portions of the electromagnetic spectrum is that they are completely useless when persistent cloud cover overlie the area of 3 interest. It is recalled that many of the early spectacular pictures from both manned and unmanned satellites were from areas of little cloud cover (c.g. Egypt, soutll\>'~stern United States, Persian Gulf. Australia). This pr0blem of persistent clouds has not been totally solved. However, in areas "'here cloud cover is aperiodic, a technique known as Composite Minimum Bright- ness (c~m) has been used to discriminate cloud from snow cover. [6,8) Because snow generally has a fairly high albedo in the visible portion of the EM spectru~ (i.e. reflectivity), it is readily seen against darker natural back- grounds. 'However, when it is obscured by cloud cover which has 'a reflectivity similar to that of the snow cover, the two cannot be distinguished from one another. In the c~m technique, the reflectance of each point over the area of interest is measured and stored in a geographic matrix'. At intervals during several days these measurements are retaken from a new image and the minimum value for each point is stored in the matrix. After the period of study is completed, the minimum values measured for each of the several points are displayed, thus forming a composite map of the minimum brightness for each point in the geographic matrix. It is assumed that during the study period the cloud cover is variable while the snow cover is essentially stable. Minimum brightnesses would represent the darker natural background (e~g. forests, vegetated land, bare ground, or, in the case of lake ice, open water or relatively young ice) while the maximum brightness would be areas of snow (or older ice) cover. Using this and similar methods, based upon'imagery from the several meteorological satellites, the boundary of the snow could be mapped to an accuracy of + 10 nautical miles, and in mountainous basins, the areal measurement ;f snow was determined to be + 5% of the measurements taken using conventional aerial photography. [8J Although effective in removing the water clouds from the scene, the CMB method may prove to be of little help in the discrimination of ice clouds, although other techniques applied over Greenland question this supposition. [9) This method of using visible wavelengths in cloud and snow discrimination on satellite imagery could be of little use in areas which are: (a) completely snow covered, as the arctic deserts or the great plains in winter or (b) areas which areperiodi- cally covered with ice clouds. In each case, several passes of the sensor are required to make the complete map. Finally, we must recognize the question of resolution when dealing with the staellite imagery. Using an ITOS image representing 90 miles (145 km) on a side and having 10 gray scales for the entire sensing range, it has been reported [10) that the lowest detectabilfty for lake ice in the eastern portion of Lake Superior ~as approximately 25% cover. Even at this coverage, there were several questionable interpretations. USE OF INFRARED: In another portion of the electromagnetic spectrum (Table 1), infrared, both near and far, have been reported to be useful ,for the determination of 4 the surface temperature of ice and snowfields. Such work is quite helpful, especially for f.101~itorin~ the advance of the firn line through the glacier season, detecting outflows from glacial lakes, the identification of snow bridges and crevasse areas .in glaciers, and to a certain degree, the iden- tification of ice/land interfaces. Thermal imagery (8.0~ to 13.5~) of s~a ice [11,12,13] can be used for the determination of ice thickness. It is assumed in this work that the water under the ice is of a constant temperature and the ice acts as an insulator. Hence, thicker ice being a better insulator, will appear cooler than will thinner ice. Highly stippled areas indicate something of the history of the ice pack through the variation of temperature, and by inference, variations in ice thickness. Recently frozen leads and • polynyas are also clearly visible. Still, such a system suffers from problems of attenuation by the atmos- phere and even for areas in which there is an atmospheric window, there is always the problem of obscuration by weather and cloud systems. TABLE 1. Wavelength Ranges of Remote Sensors Spectral Region Wavelength Frequency (Hz) Visible 9.380 O. 780~ 7.89_1014 to 3.85_1014 Infrared: 3.85_1014 1_1014 Near 0.780 3.000~ to Intermediate 3.000 8.00011 1_1014 to 3.75_1013 Far 8.000 1000l! 3.75_1013 to 3_1011 Microwave 3-1011 3_1010 Millimeter 0.1 1.0 cm to Centimeter 1.0 10 em 3_1010 to 3_109 Decimeter 10 100 cm 3_109 to 3_108 (after [l4J, p. 75) THE MICROWAVE REGIONS: The longer wavel~ngths ranging from 0.1 cm to 1.0 m are generally . termed microwaves. These waves lie between the most familiar E}! waves, that is, between the visible and the radio wave lengths. One of the more important features of these 'radar waves' is their ability to retain both their strength and their form while propagating through·. the atmosphere of the earth. [15] In addition, in an active system (e.g. radar) which is transmitting a signal of known strength and measuring the strength of the reflected (i.e. returing) signals, the measurements are independent of available light or other (natural) radiated energy. Thus radar, compared to i i . I 5 the visible and IR portions of the spectrum, while suffering very little attenuation by the atmosphcre or cloud cover and in combination with the independence of natural light sources, is virtually an all weather dayl night system. Radar is a scanning device, that is, it scans orthogonally to the air- craft flight path ovcr an area of several miles width. The samples of backscattered energy (i.e. the refl~ction of the transmitted signal) are easily measured and converted into a gray-tone series for the production of hard copics. The information ca~ also be readily stored on computer compa- tible tape. This is an additional advantage radar has over conventional aerial photography. Although this advantage is also recognized for other line scan devices (as the multi-spectral scan~er), the width of swath covered by radar is much greater thus affording more ground coverage per aircraft pass and hence less time per unit area of ground coverage for data collection. RADAR IMAGERY: Although the resulting radar imagery appears similar to aerial p'hoto- graphs, there are several subtle differences. One of the major differences is in the projection. For an optical projection, all points from the imaged surface to the imaging surface are projected through a common point in the lens, via straight lines.' Thus both azimuth and range points are simultane- Qusly.reco.rded. In the radar projection, on the other hand, the imaged surface is transformed to the im~ing surface through a series of constant range (i.e. constant distance from the antenna) arcs. For recording in the azimuth direction, the film is advanced in the recorder at a rate propor- tional to the speed of the aircraft and each line of points (in the azimuth direction) is plotted next to the previous one. Thus, there is a uni- formity of scale in the along-track direction (that is, parallel to the aircraft line of flight). However, in the range direction (perpendicular to the line of flight), the scale is continually changing and is therefore similar to, but reversed, when compared to an oblique aerial photograph. (~.~. In radar the scale decreases at near range, for oblique photographs, at far range.) . Hence, the two resulting images are different and should be viewed quite differently. Radar images and oblique photos also show a similar relief displacement, with points of high elevation displaced toward the radar set, a feature termed 'layover' These and similar comparisons of SLAR and aerial photographic imagery are discussed in the literature. [15,16] Early radar imagery consisting of photographs of PPI-scopes, showing ice in' the Gulf of St. Lawrence is also available. [17] TIiE ~\DAR EQUATION: wnat exactly does the radar measure? For this brief discussion, we must S • 6 return to the basic considerations of the radar equation, the equation which describes the interaction of the surface (i.e. the 'target') with the emitted ~lcrowave signal and its return to the radar antenna. The radar equation, as defined in [18], is: p t G2ot.. ,2 (41f}3 R4 in which: S is the received power Pt is the transmitted power ~ is the wave length of the emitted EM wave a is the echoing (scattering) cross-section R is the range. Within this equation, the scattering cross-sectionl is a function of many conditions, and it is essentially the only term which is target dependent. When this is brIefly considered, we note that by determining the controlling factors of the scattering cross-section, we would be able to approach the identification of the variables on the ground and hence the identification of the imaged items. These controlling factors in the scattering cross-section are: (l) SYSTEM PARA}lliTERS: (a) wavelength; (b) polarization; (c) illuminated area; 'and:(d}'lHrection of illumination (azimuth and elevation) and (2) GROUND PARAMETERS: (a) complex permitivity; (b) surface roughness; and (c) roughness of the -subsurface to depth where attenuation reduces the wave to negligible amplitude. [20,21] '" ,.,' The geometry of the target in terms of surface ro~ghness has a very important role in the strength of the radar echo. For example, a smooth surface will provide no radar return because all signals reaching the surface will be reflected specularly, that is, in accordance with the Fresnel- reflection law (i.e. angle of incidence equals angle of reflection). The only occasion when such a smooth surface would produce a signal return would be when the impinging radar signal is orthogonal to the target surface. Hen~e. in many radar images, water areas appear black or, if covered with small waves, speckled. A surface which would appear rough at X-Band (3 em) may appear smooth at S-Band (5.8 - 19 cm) or L-Band (19 - 77 em). In sea ice, roughness is often correlated with the age of the ice, with the older ice being increasingly rougher. By measuring roughness, as has been done using both scatterometers and radar imagery, a very good indication of the ice age, and by inference, the ice thicknes!i has been developed. [22] Roughness as it affects the gray scale was also an important contributing factor in the analysis of JO~SON & FARMER. [23] lThe scattering cross-section is the measure of the ability of a target to produce a return. It is equivalent to the area of an isotropic scatterer which would produce a radar echo at a sensor equal to that from a given target. [19] 25 / 7. However, for lake ice on the mid-latitude Great Lakes, we do· not have· this advantage. Ice is generally very young with the oldest being possibly f~ur months, and consequently the surface roughness has not had sufficient ti~c to develop. Surface roughness is rather the result of drifting snow or pressure within the ice body. If we take an ideal case, tha~ of a homogeneous plane and if we assume that the radar l~oks at this plane from a single angle and has constant system parameters, we have reduced the number of unknown terms in the scat- tering cross-section to essentially one, that is, the complex p~rmitivity or dielectri~ constant of the target. This is, of course,. an abstraction for ~uch of the real world, but may not be too far from reality with respect to some snow and ice studies. The dielectric constant of ice is quite low (in the neighborhood of 3) and for snow is almost equally low. EVANS [24] has noted that dielectric variations are dependent upon: (a) density of the snow and ice; (b) wave- length; (c) temperature of the target; (d) Formzahl number2; (e) impurities in the snow or ice; and (f) free water content. Although laborat~ry work needs to be done concerning the dielectric constant of snow and ice, little work has been conduct~d using samples of natural materials. The relative importance of these variables in determining the dielectric constant is unkno~~, and the relative importance of the dielectric constant in deter- mining the scattering cross-section is almos~ certainly unknown. It has been previously suggested [25] that the sea ice/glacier ice inter- face should be easily determined by electromagnetic means because there is a distinct change in the dielectric constant across this interface. This is probably one of the best examples where imaging radars will-be'useful, Likewise, bergs in a pack of frozen sea ice could conceivably be easily spotted using the same logic. An exceptionally good paper dealing with imagery of sea ice is presently available. [23] IMAGERY OF GREAT LAKES ICE: Our experience at ~illow Run Laboratory.has shown, however, that X-Band radar imagery can be very helpful in distinguishing clearly and definitively, several types of Great Lakes ice. [26,27] Figures 1 and 2 clearly show several types of ice, classed generically, which were observed in the south- eastern portion of Lake Superior during the 1967-1968 winter season. In figure 1 brash ice, open water, large floes and thrust features are clearly .. 2rorozahl is defined as a single parameter used to show how one medium is dispersed in another; essentially it is relatec ~o crystal orientation and structure of the snowpack with F = 0 when crystals are all oriented normal to the elect~ic field and F = 00 in the other extreme (i.e. orientation normal to the fiele) case. Hence, when dealing with snow, the structure of the snow pack is of extrerr.e importance. [23] . 8 seen. Also, easily identified are shore ice ridges which have developed along the entire portion of Whitefish Point which has a northern exposure. In Figure 2 several additional features of ice breaker channels, snow drifts on older ice, open water resulting from the parting of a large floe and recently refrozen ice are seen. The linear feature labeled "refrozen leads/cracks" is very white, signifying a high radar return and may have been a misinterpretation of a large pressure ridge. To a degree, ice thick- ness can be inferred in some areas, for example, -in the area identified as "thrust features" (Figure 1). These highly irregular cracks are common features in thin ice, whereas the possible pressure ridges in Figure 2 are experienced on thicker and older ice. However, at this time we are unable to state quantitatively the ice thickness indicated by such features. CONCLUSION: From the several images shown here, it is noted that there is a great potential for expanded usefulness of radar -imagery in the field of ice hydrology. It is theoretically possible for some very subtle features to be identified using radar imagery. This would give us a remote sensor capable of acquiring both area and point data of a nature which is at present only available on a point sample basis, or, if aerial photography is used, when weather and lighting conditions would permit. Radar will -nflt, however,solve all data acquisition problems for the snow and ice hydrologist, even when the present problems of relating the scattering cross-section to the target parameters are solved and we develop a more extensive interpretation key. Ice thickness data, for example, are not presently discernible using existing airborne imaging radars and even with longer wave microwave instru- ments. water layers in the ice together with variations of the dielectric constant through the ice. sheet' are problems which tlust be more thoroughly understood in order to develop a reasonable model of the ice body. When this model is available, we can return to our interpretation ·of radar ice imagery and possibly extract additional information concerning other important parameters of fresh water lake ice. It is expected that as shipping interests continue to search for methods of expanding the shipping season in the upper Great Lakes-, quick, efficient and reliable ice information collection systems will be required as an input for their daily decision making. Radar flights over the pro- posed shipping routes can collect these data, independent of the weather; and at a scale and resolution sufficiently fine to be an important aid to navigation. Like~ise, the scientist interested in area and location, together with types, of ice cover can expect to find radar to be a useful field tool for his work. 2'7 I ·oi. i, "-'--" ··_·· ..·~·~~·~------__ L 9 . REFERENCES: [l) CO~INONER, B. (1971). The closing circle: Nature, man and technology, A. A. Knopf, New York. [2) COOPER, C. F. (1965). Snow cover measurement. Photogramm. Engng., 31, pp. 611-619. [3) BAfu~ES, J. C. & C. J. BOh'LEY (1968). Snow cover distribution as mapped from satellite. Wat. Resour. Res., 4, pp. 257-272. [4) BAfu~ES, J. C. & C. J. BO~'LEY (1970). The use of environmental satellite data for mapping annual snow-extent decrease in the western United States. Concord, Nass., Allied Res. Assoc., Inc. Final Report (Contract E-252-69(N». [5) FRITZ, S. (1963). Snow survey from satellite pictures. Proceedings, First International Symposium on Rocket and Satellite Meteorology, 23-25APR62. H. WEXLER &J. E. CASKEY, JR. (Eds.), J. Wiley and Sons (Interscience), New York, pp. 419-421. [6) SABATINI, R. R., ~~. (1971). Nimbus earth resources observations. Concord, Mass., Allied Res. Assoc., Inc. (Contract NAS 5-2l6l7).xviii+265 pp . . [7) ZAITZEFF, J. B. & J. W. SHERMAl~, III (1968)'. Oceanographic applications of remote sensing. P~oceedings, Fifth Symposium on Remote Sens. of Env. The U. of Michigan Institute of Science and Technology, Willow ."Run "'Labs. SEP., Ann Arbor, Michigan, pp. 483-495. (8) McCLAIN, P. & D. R. BAKER (1969). Experimental large scale snow and ice mapping with composite minimum brightness charts. ESSA Tech. Memo. NESCTM-12. [9] HAUTH, F. F. &J. A. \~INMAN (1969). Investigation of clouds above snow surfaces utilizing radiation measurements obtained from the Nimbus Ir satellite. Remote Sens. Env., 1, pp. 7-11. [10] MARSHALL, E. W. & P. E. CHASE (1972). Interpretation of ITOS satellite imagery of Great Lakes ice and snow cover. Paper presented at Fifteenth Conference on Great Lakes Research, 05-07APR72, Madison, Wise. [11] McLE~~, J. H. (1965). Infrared sea ice reconnaissance. Proceedings, Fourth Symposium on Remote Sens. of Env. The U. of Michigan Institute of Science and Technology, Willow Run Labs. NOV., Ann Arbor, Michigan, pp. 789-798. (12) HORVATH, R. & D. S. LOlfE (1968): Multispectral survey in the Alaskan Arctic. Proceedings, Fifth Symposium on Remote Sens. of Env. The U. of Michigan Institute of Science and Technology, Willow Run Labs. SEP., Ann Arbor, Michigan, pp. 483-495. (13) HORVATI{, R. & W. L. BROh~ (1971). Multispectral radiative characteris- tics of Arctic sea ice and tundra. The U. of Michigan, Institute of Science and Technology, Willow Run Labs. Report No. 27980-2-F; JUL., Ann Arbor, Michigan. [14) Nat. Res. Council. (1970). Remote sensing: With special reference to agriculture and forestry. Nat. Acad. Sci.-Nat. Res. Council, Washington, D. C. xviii+424 pp. SESSION: UNESCO-5 • (27J [20] (15] 124J [25] (26] 10 INNES, R. B. (1968). An interpreter's perspective on modern airborne- radar imagery. Proceedings, Fifth Symposium on Remote Sens. of Env. The U. of Michigan Institute of Science and Technology, Willow Run Labs. SEP., Ann Arbor, Michigan, pp. 107-122. (16] LEONARDO, E. S. (1963). Comparison of imaging geometry for radar and camera photographs. Photogramm. Engng., 29, pp. 287-293. [17] CA}ffiRON, H. L. (1964). lee-cover surveys in the Gulf of St. Lawrence "by radar. Photogramm. Engng.; 30, pp. 833-841. [18] BERKOIHTZ, R. S. (1966). Modern radar: Analysis, evaluation and system design. J. Wiley and Sons, New York. xv+606 pp. [19] UCLA (1968). Remote sensing of environment, intensive two-week short course, 05-l6AUG68. Sponsored by the Eng. & Phy. Sci. Extension and TRW Systems, Los Angeles. (NTIS Microfiche DN70-14072). GUlNARD, N. W." (1969). The remote sens ing of the sea and sea ice. Proceedings, Sixth Symposium on Remote Sens. of Env. The U. of ~lichigan Institute of Science and Technology, Willow Run Labs. OCT., Ann Arbor, Michigan, pp. 737-754. MOORE, R. K. (1969). Radar return from the ground. Engng. Bull., 59, U. Kansas, Lawrence, Kansas. 87 pp. ROUSE, J. W., JR. (1969). Arctic ice type identification by radar. Proceedings IEEE, 57, pp. 605-611. JOHNSON, J. D. & L. D. FAR}ffiR. (1971). Use of side-looking radar air-borne radar for sea ice information. J. Geophys. Res.; 76, pp. 2138- 2155. " EVANS, S. (1965). Dielectric properties of ice and snow: A review. J. Glacio1., 5, pp. 773-792. RAGLE, R. H., R. G. BLAIR, & L. E. PERSSON. (1964) . Ice core studies of Ward Hunt Ice Shelf, 1960. J. Glaciol, 5, 39-59. LARROWE, B. T. ~ al. (1971). Fine-resolution radar investigation of Great Lakes ice cover. The U. of Michigan, Institute of Science and "Technology, Willow Run Labs. Report No. 1900-l-F. JAN., Ann Arbor, Michigan. viii+179 pp. LARROIfE, B'. T. ~ a1. (1971). Lake ice surveillance via airborne radar: Some experimental results. Proc~edings, Seventh Symposium on Remote Sens. of Env. The U. of Michigan Institute of" Science and Technology, Willow Run Labs. MAY, Ann Arbor, Michigan, pp. 511-522. [21J "[22] (23] ". ---_._-..... ..~ .. ' I .; ·1, • . .... ';''';':'~ ~ .:-:-... ~;~I-~:,~. ·~1 I' .:..:".~... \ . .........~ ..~.}-.-' ~:;',. .'1 . :.,; .' '1 .•!._..._ ....~ _..- '.• '--' ~:-.i;-;'.' ~ -I LAKE SUPERIOR \ ._-------- .t f· '. ;. .. ". "-r t-., ... _ .. I .. ' . iI', -