The detector is thermo-electrically temperature stabilized. Incident solar radiation is collected by a sensor on the top of the aircraft and fed to the spectrometer in an additional 20 pixels so that a full spectrum of incident solar radiation is recorded with each scan to allow post processing computation of apparent reflectance. Differential global positioning data and inertial aircraft attitude information are recorded with each scan to allow geo-referencing each scan during post processing.
In post processing by the 3DI company the spectral observations were converted to reflectance at the aircraft level by using the in-flight observations of incident solar radiation. Image reflectance, over the range 0 to 1.0, is scaled in integers from 0 to 10,000. Since the observations are quantized in 12 bits, each bit is equivalent to 2.44 reflectance units. This level of precision is often described as 3 ½ significant digits.
In-flight observations of differential GPS and aircraft motion were used to georeference the position of the observations and correct for aircraft motion. The flight strip data were delivered as generic binary files referenced to UTM, meters, Zone 18.
Table I-1 shows the spectral channels assigned for this flight. Note that the gain of the shorter wavelength bands was increased to compensate for lower sensor sensitivity in that spectral region. Doing so resulted in observable noise in the data of bands 1 to 4.
Table I-1
Wave-band | AISA Chan | - | Min. wvl | Center wvl | Max. wvl | Chan. width | Avg. offset | Avg. gain |
1 | 22 | 4 | 458.54 | 461.78 | 465.02 | 6.48 | 0 | 26.5205 |
2 | 29 | 4 | 469.89 | 473.13 | 476.37 | 6.48 | 0 | 22.9378 |
3 | 35 | 4 | 479.61 | 482.86 | 486.1 | 6.48 | 0 | 18.4235 |
4 | 41 | 4 | 489.34 | 492.58 | 495.82 | 6.48 | 0 | 14.5105 |
5 | 47 | 4 | 499.07 | 502.31 | 505.55 | 6.48 | 0 | 11.8414 |
6 | 53 | 4 | 508.79 | 512.03 | 515.28 | 6.48 | 0 | 10.0721 |
7 | 59 | 4 | 518.52 | 521.76 | 525 | 6.48 | 0 | 8.8712 |
8 | 66 | 4 | 529.87 | 533.11 | 536.35 | 6.48 | 0 | 7.8921 |
9 | 72 | 4 | 539.59 | 542.83 | 546.08 | 6.48 | 0 | 7.2363 |
10 | 78 | 4 | 549.32 | 552.56 | 555.8 | 6.48 | 0 | 6.6292 |
11 | 84 | 4 | 559.17 | 562.55 | 565.93 | 6.76 | 0 | 6.1127 |
12 | 90 | 4 | 569.31 | 572.69 | 576.07 | 6.76 | 0 | 5.7445 |
13 | 96 | 4 | 579.45 | 582.83 | 586.21 | 6.76 | 0 | 5.553 |
14 | 102 | 4 | 589.59 | 592.97 | 596.35 | 6.76 | 0 | 5.5433 |
15 | 108 | 4 | 599.73 | 603.11 | 606.49 | 6.76 | 0 | 5.6339 |
16 | 114 | 4 | 609.87 | 613.25 | 616.63 | 6.76 | 0 | 5.704 |
17 | 125 | 4 | 628.46 | 631.84 | 635.22 | 6.76 | 0 | 5.6234 |
18 | 137 | 4 | 648.74 | 652.12 | 655.5 | 6.76 | 0 | 5.2642 |
19 | 149 | 4 | 669.02 | 672.4 | 675.78 | 6.76 | 0 | 4.8171 |
20 | 155 | 4 | 679.16 | 682.54 | 685.92 | 6.76 | 0 | 4.6681 |
21 | 161 | 4 | 689.3 | 692.68 | 696.06 | 6.76 | 0 | 4.6157 |
22 | 167 | 4 | 699.44 | 702.82 | 706.2 | 6.76 | 0 | 4.6444 |
23 | 172 | 4 | 708.45 | 711.97 | 715.49 | 7.04 | 0 | 4.6891 |
24 | 178 | 4 | 719.01 | 722.53 | 726.05 | 7.04 | 0 | 4.7774 |
25 | 184 | 4 | 729.57 | 733.09 | 736.61 | 7.04 | 0 | 4.9535 |
26 | 189 | 4 | 738.37 | 741.89 | 745.41 | 7.04 | 0 | 5.1291 |
27 | 195 | 4 | 748.93 | 752.45 | 755.97 | 7.04 | 0 | 5.3861 |
28 | 212 | 4 | 778.85 | 782.37 | 785.89 | 7.04 | 0 | 6.2647 |
29 | 227 | 3 | 805.25 | 807.89 | 810.53 | 5.28 | 0 | 9.4876 |
30 | 246 | 3 | 838.69 | 841.33 | 843.97 | 5.28 | 0 | 11.2467 |