FRONTISPIECEReproduction of a portion of a semi-eontrolled SLAR mosaic. JANW. VAN ROESSEL Earth Satellite Corp. Berkeley, Cali$ 94704 ROGERIOC. DE GODOY Ministerio das Minus e Energia Rio AJaneiro GB, Brazil SLAR Mosaics for Project RADAM Semi-controlled mosaics made with side-looking radar imagery comprise one of the mapping products of the Amazon and the Brazilian Northeast. (Abstract on next page) INTRODUCTION a standard map product with a certain NTIL THE organization of Project ADA AM (for geometric accuracy. U~adar~mazon) in October 1970, the To date, the minor o1,jective has almost Brazilian Amazoil Basin was one of the been acco~nplished:160 semi-controlled SLAR largest poorly mapped areas in the world. At mosaic sheets have been released for pul~lic that time, however, the Brazilian government use. Each inosaic sheet covers a rectangular decided to undertake a reconnaissance sur- area of 1 degree latitudinally by 1.5 degrees vey of the Amazon and the adjacent Brazilian longitudinally. Preliminary checks have in- Northeast in a most unconventional manner, dicated that the geometric accuracy of each namely, by executing the largest commercial sheet and of the overall nlosaic can be ex- side-looking radar (SLAR)remote-sensing proj- pected to be well within the contractual re- ect ever undertaken. quiren~ents,which will be described pres- The major objective was to collect informa- ently. tion on mineral resources, soils, vegetation, Mapping such an extensive area in such a and land use; a minor objective was to obtain short period required an uncoilventional PHOTOGRAMMETRIC ENGINEERING, 1974 mapping tool, for which only SLAR qualified reliable cartographic delineations, a certain because of its capability to penetrate clouds. minimum data quality had to be achieved. Indeed, the pay-off has been proportional to This minimum level was at least maintained the high risk taken in the use of a commer- by observing technical specifications in- cially unproven mapping device, to the effect cluded in the data acquisition contract in the that a good set of reconnaissance maps is now form of a Technical Annex. Many of the initial available for all of Brazil north of the 8"s technical specifications were provided by parallel. Dr. S. B. Levin of Earth Satellite Corpora- In this paper we shall briefly discuss the tion. background of Project RADAM (de Azevedo, A special team (ApoioTbcnico) was formed 1971) as well as the contractual requirements to work jointly with the contractors to and the project instrumentation, and we shall evaluate image quality and geometric fidelity then consider in somewhat more detail the of the radar imagery, and to implement SLAR specific SLAR geometry, ground control con- mosaic compilation methods. siderations, semi-controlled mosaic compila- Some highlights of the SLAR quality re- tion and accuracy evaluation. quirements are the following: IMAGE QUALITY PROJECTRADAM Dynamic range 20 dB; resolution 16 M. The project is supported mainly by the * Brazilian Ministry of Mines and Energy. The GEOMETRIC FIDELITY OF IMAGE STRIPS initial plan covered an area of about * Along-track and across-track scales uniform 1,500,000 km2, but the project was gradually within 1 percent. ABSTRACT:Semi-controlled SLAR mosaics covering most of Northern Brazil (more than 4,500,000 km2) are being compiled as a part of Project RADAM of the Brazilian Ministry of Mines andEnergy. These mosaics represent the first large-scale commercial effort to manufac- ture maps from SLAR imagery. A special combination of SLAR in- strumentation and airborne and ground navigation equipment is used for the project, creating special metric problems with respect to ground control, flight configuration mosaic compilation and accu- racy estimation. extended to cover approximately 4,600,000 * Along-track scales of adjacent strips consis- km2. This extension was made possible by tent within 1 percent. the successful performance of the system. * Angular distortion not to exceed 10 mrads in The project area is shown in Figure 1. any one swath. * Image sidelap average 25 percent but not to For acquisition and processing of the radar be less than 10 percent at any point. imagery and related remotely sensed data, a contract was signed with two associated en- GEOMETRIC FIDELITY OF SEMI-CONTROLLED MOSAICS terprises: LASA Engenharia e ProspeF~oes * Cumulative scale discrepancy in any direc- S. A. and Aero Service Corporation. Aero tion not to exceed 1 km. Service's role was mainly to obtain the radar Angular distortion not to exceed 10 mrads imagery, whereas LASA provided logistical within any one mosaic. planning, executed the ground survey and * Comer positions of each mosaic to be accu- assembled the radar images into mosaics. rate to within 1 km with probability of 95 Earth Satellite Corporation was contracted percent and to within 0.5 km with probabil- by the Brazilian Government to select and ity of 50 percent. evaluate proposals made by qualified con- * Tic mark grid orientation to be correct within 10 mrads. tractors, to provide the contractual and tech- nical specifications for the project, and to ad- vise Project RADAM on matters of quality con- trol and imagery interpretation. RADAMflights were spaced 15 min of arc apart and were generally flown North-South. The flight spacing provided 25 percent To permit a homogeneous interpretation of sidelap for the radar strips and 8 percent the area's natural resources and to provide sidelap for concurrently obtained infrared SLAR MOSAICS FOR PROJECT RADAM LEGENDA ARLI COY COBEIITUR~ TOTAL SHORAN FIG.1. The project area superimposed on the outline of Brazil. The cross- hachured area was controlled through E-W tie lines. Triangles indicate TRANSIT points. photographs which were taken with 66 per- Inertial guidance platforms-2 Litton cent forward overlap. For the initial area all LTN-51 systems, indicating present posl- flights were tracked with SHORAN For the tion, attitude, heading, drift angle. and add-on areas, a new and less expensive ground velocity. Radar altimeter-Stewart Warner APNl195. ground configuration was adopted for which Accuracy +. 50 m. only East-West tie lines were tracked with Barometric differential altimeter SHORAN Figure 1 shows the extent of the ini- -Rosemount 803C. tial and the add-on areas, as well as the con- SHORAN master station-RCA APN-84. figuration of ground control points. Digital data handling equipment-Lancer The remote-sensing platform was a twin- digital data system. Kenedy tape recorder. jet Caravelle flying at an altitude of 12 km Monroe datalog printer. with a speed of approximately 690 kmthour. The digital-data system integrates the iner- On board were the following remote sensing tial velocity signal and triggers the cameras and navigation devices: and the fiducial marks on the SLAR imagery for Side-looking radar-Goodyear Mapping every 10 kilometers. On digital tape are re- System 1000 (GEMS).Optically correlated, corded the SHORAN ranges, the LTN-51 out- coherent, and focused beam. Ground puts, the radar altimeter outputs and the time, range presentation. Operational one record per km. parameters-scale 1:400,000, ground range To provide ground support for the SHORAN delay 11 km, ground sweep 37 km, swath system, accurate point positions for 45 overlap 25 percent. ground points were determined using TRANSIT Aerial cameras-Zeiss RMKA 23/85 satellite locating equipment. The Magnavox super-wlde angle, used with color-infrared film and W15 filter. 12S Mark I camera used MX-702 provides coordinates accurate to with B&W infrared film and47,57,25A, and within 15 meters. A few observations were 89B filters. on points of known coordinates adjusted to Video tape system-3 cameras Javelin the Brazilian Corrego Allegre datum (HIRAN SC-950 with Sony videotape recorders. points). The discrepancies due to the differ- PHOTOCRAMMETRIC ENGINEERING, 1974 ences between the Brazilian and satellite el- At the same time the slant range r is lipsoids were alinost constant, namely, l sec- situated in the X'Z1-plane for which we can ond for latitude and 3 seconds for longitude write the following equation: (da Rocha, 1971). The SH~RANsystem was not used in the usual manner, namely for the determination of base distances between ground stations, where but instead the recorded ranges to two ground stations with known coordinates A' = sin K cos 4 + sin 4 cos K sin w, were used to intersect the air-station posi- B' = COS K COS w tions. C' = -sin 4 sin K + cos K sin w cos 4 Logistics plans called for the operation of four SHORAN transponders at a time so that one with K, 4 and o representing the yaw*, roll spare transponder was always available. and pitch angles, respectively, ofthe antenna Considering that a great number of ground pod. stations were located in uninhabited regions, If we assume that Zc is the flying height and that flight operations were almost con- above the plane in which P is situated, then Z tinuous, the sinall amount of untracked flight = 0, so that Equations 1and 2 reduce to two lines (16 percent) indicates a high perfor- equations with two unknowns, from which mance level of the SHORAN system and its we can solve for X and Y, namely operating crew. In all, 300 flight missions were made, ac- X =A1C'Zc? B'. counting for a total of 1,500 hours of flight [(r2 - Z2,) (ArZ+ Brz) - ~'~22~1'+ X,; time. Af2+ Bt2 SLAR GEOMETRY and by permutingAf and B' in Equation 3 we It was the task of the Apoio Tbcnico team to obtain the expression for Y. Considering the monitor the quality and geometric fidelity of look direction, there is no difficulty in iden- the incoming iinages and also to advise on the tifying the proper solution. implementation of mosaic colnpilation Formula 3 and its Y equivalent can be used methods.