The processor on board the satellite samples the real-time AVHRR data to produce reduced
resolution GAC data. Four out of every five samples along the scan line are used to compute
one average value, and the data from only every third scan line are processed. As a result, the
spatial resolution of GAC data near the subpoint is actually 1.1 km by 4.4 km with a 3.3 km gap
between pixels across the scan line, although generally treated as 4 km resolution. All of the
GAC data computed during a complete pass are recorded on board the satellite for transmission
to Earth on command. The 10-bit precision of the AVHRR data is retained. Table 8.3.1.4.1-1
summarizes fundamental characteristics of the data.
Table 8.3.1.4.1-1. GAC Data Characteristics.
|
Parameter |
Value |
|---|
| Sample word size |
10 bits |
| Number of sampled channels/available channels |
5/6 |
| Number of Earth samples per scan |
409 per channel |
| Scan rate |
120 scans per minute |
| Scan direction |
East to West (northbound) |
| Instantaneous Field of View (IFOV) |
0.07449 degrees (all channels) |
| Spatial resolution at nadir |
4.36 km (cross track average) by
1.09 km (along track) at 833 km
altitude |
| Cross track distance between sample centers at nadir |
5.45 km at 833 km altitude |
| Along track distance between sample centers at nadir |
3.27 km at 833 km altitude |
| Cross-track scan coverage |
± 55.4 degrees from nadir |
| Swath width |
2,399 km at 833 km altitude |
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