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3.1 Signal to Noise Ratio 
The end to end system requirement for SNR is 10: 1 forthe pan system. This is for a target contrast ratio at the 
entrance aperture of 2 to 1, measured at the Nyquist frequency, with 24 TDI. The MS SNR's are spec'd at 13.0, 
14.0, 11.5, and 13 to 1 for the blue through NIR bans respectively. The measured SNR for the pan band is 14 to 1 
average with a variance of 1.0. The MS band SNR's at nyquist are 24, 40, 30, and 18 to 1. The corresponding flat 
field SNR's for the MS bands 1 through 4 are: 94, 143, 103, and 67 to 1 respectively. The measured noise across 
all five bands is about 4 digital counts, making the system shot noise limited. All specs and measured data are 
without transfer function compensation, MTFC. 
32 Radiometric Calibration 
The on-orbit radiometric calibration of the IKONOS system is performed in three ways. First, a passive on- 
board calibration assembly is used to fully and uniformly irradiate the focal plane sequentially through a series of 
Waterhouse stops in the calibration assembly, using the sun as the source. The range in size of the aperture stops 
provides for calibration data over the full dynamic range of the multispectral detectors and pan detectors for all 5 
TDI settings. This processed calibration data results in a five point cal curve per detector per TDI setting. At this 
time it is too early to have sufficient data to measure the absolute or temporal radiometric accuracy. However, 
there are no indications that the system will not meet the spec value of 10%. The relative accuracy was measured 
using four stars, one of which was questionable, to verify that the system is equal to or better than the 5 % 
relative accuracy spec. The linearity is specified at 5% of full scale. The measured value is in the order of tenths 
of a percent, and when calculated as a percent of the measured value, about 2% on the average. Figure 8 depicts 
the result of the gain adjusted cal curve for the multispectral bands using this data. The preliminary QSE’s for the 
MS bands, using this very limited data set are: 132.17, 151.79, 146.07, and 138.17 electrons per digital count. 
MSI StarCal - Post-Adjustment 
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Expected Stellar In-Band Counts 
Figure 8 Multispectral calibration from star data 
3.1 Metric Accuracy Assessment 
The IKONOS satellite system was designed to meet the metric accuracy requirements specified both with and without the 
use of ground control points, GCP's. 
3.1.1 Stereo Accuracy without Ground Control 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 133