Frank Gerlach
2.2 Panchromatic Sensor
The pan sensor consists of 13,816 unique detectors with 5 ground commandable time delayed integration, TDI,
modes to control exposure over a wide dynamic range of input radiance’s. TDI is not changed within an image,
For the present nominal TDI setting being used by IKONOS, the exposure time is 2.7 milliseconds. The pan
CCD's employ a two phase architecture, limiting linear smear due to individual pixel integration to 0.5 pixels.
The well capacity is 200,000 electrons, with an average quantum efficiency, QE, of 0.35. The pan CCD spectral
QE curve is shown in figure 2. The quantization step equivalence, QSE, represents the exposure change
produced by a single quantization step change out of the A/D converter. Although 11 bits equates to 2048 counts,
only 1800 are used. For the pan band, at a TDI of 24 steps, a 40 degree solar elevation, 80% target reflectivity,
and 20% background reflectivity, results in an input radiance at the aperture of 8.44 mW/cm/sr, or a nominal QSE
of 0.55 micro Joules / sq. meter and 170,000 electrons. The nominal QSE is 94.4 electrons
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Relative Spectral Response
350 450 550 650 750 850 950 1050 1150
Wavelength (nm)
Figure 2 Pan CCD relative spectral response
Figure 3 shows the typical resolution of the IKONOS pan imagery. Note people in the square.
2.3 Multispectral Sensor
The bandpasses of the multispectral sensor are intended to be similar to those of the Landsat Thematic Mapper,
Bands one through four.
Band 1! Blue 0.45 - 0.52 micrometers
Band2 Green 0.52 — 0.60
Band3 Red 0.63 - 0.69
Band4 NearIR 0.76 - 0.90
Figure 4 shows the relative spectral response for the four multispectral filters.
The multispectral detectors have a well capacity of 250,000 electrons, with a one phase arcitecture.
For the multispectral band, the QSE's for bands 1 through 4 are 100.0, 100.6, 72.2, and 109.2 electrons.
130 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.
31
