These data, for a single pass over the station, represent approximately 
10 minutes recording time; that is equivalent to 4000 km on the ground. 
The recorded tapes are transshipped for processing to the Jet Propulsion 
Laboratory in Pasadena, California, where the radar data are optically 
correlated on the SAR Data Processing System (SDPS) shown in Fig. 3, after 
receipt of the SAR supplementary data record (SDDR). The SDDR data set 
consists of information on the satellite's altitude, attitude and geometric 
location referenced to spacecraft time, and on operational characteristics 
of the SAR. 
DATA ACQUISITION 
On the basis of the 4% duty cycle resulting from the power and thermal limi- 
tations of the sensor, 6,000 opportunities to record SAR data at ground 
stations will occur. The five stations capable of acquiring SAR signals are 
at Fairbanks, Alaska (ULA), Goldstone, California (GDS), Merrit Island, 
Florida (MIL2), Shoe Cove, Newfoundland (SNF), and at Oakhanger, England, 
the masks for these stations are shown in Fig. 4. The U.S. stations are 
part of NASA's Satellite Tracking and Data Network (STDN) operated from the 
Goddard Space Flight Center. Station loads for recording SAR data vary as 
a function of orbit/latitude considerations, and, as such, the highest 
number of passes will be recorded at Fairbanks, as the nadir track of the 
spacecraft become tangential to the 72? parallel. 
The data acquisition scheme is based on two factors. First, the 108° 
inclination baseline orbit and the superimposed stepping logic, described 
in Ref. 2, and shown in Fig. 5, defines coverage possibilities for SEASAT-A. 
Guided by requirements for evaluating the marine geoid with ALT data, the 
uniform equatorial crossings at a spacing of 927 km during the first 3 days 
will be followed by a west-to-east progression of this spacing 18.5 km 
distant from the nearest track laid down 3 days before. This sequence is 
known as the Baseline orbit, shown in Fig. 6 for a 60-day period. However, 
considering the potential for synoptic oceanography, other rapid global coverage 
has generated an alternate stepping sequence of 25 days (Fig. 7) known as the 
Cambridge orbit (Fig. 8). The Baseline orbit is firmly established for the 
first year of operations plus 30 days, and the Cambridge orbit may be made 
operational the second year. Addition of the 30 days results from including 
a calibration period for the ALT, wherein the orbit will be "frozen" into 
its basic 3-day repeat cycle during September 1978. 
The second factor is the fine-tuning of the coverage requirements for SAR 
data in view of existing engineering constraints. Although thermal and power 
considerations limit the number of opportunities to record the radar data, 
recording costs further constrain the actual number of minutes of data 
that will be acquired. Relative to the STDN stations, 15,000 minutes of 
SAR data will be entered onto high-density digital tapes, that, on the basis 
of an average of 10-minute long passes over the stations, represents 
1500 passes per year. The Canadian and European stations will acquire 
additional amounts of data and provide, on request, copies of their tapes