SENSOR CHARACTERISTICS

1-3 SENSOR CHARACTERISTICS

1-32 Radiometrical characteristics

  • The radiometric resolution gives the smallest radiance or reflectance which is detected.
  • The radiometric calibration which insure that measurements taken in the same image, in different spectral bands or at different times are consistent.

1-321 Radiometric resolution

    The radiometric resolution is expresses in terms of Noise Equivalent Difference of Reflectance (NEdR) that is detected within reflectances for each spectral bands.

    The ranges for surface reflectance (allowing for saturation for some land covers as snow or bright soils in some conditions or spectral bands and for clouds) are consistent with usual reflectance values:

      Spectral Band

      Surface reflectance range

      RED

      0.0 - 0.5

      NIR

      0.0 - 0.7

      SWIR

      0.0 - 0.6

      BLUE

      0.0 - 0.5

    The surface reflectance resolution is of the order of 0.001 to 0.003 with some adjustments for the different bands :

    • for the red band, as vegetation ground reflectances are low (generally less than 0.1), the NEdR is of 0.001 for reflectance up to 0.1 for analysis on small blocks of pixels corresponding to areas of about 10x10 km. The value for NEdR increase linearly up to 0.003 for reflectances values of about 0.5.
    • for the NIR and SWIR bands, reflectance differences of 0.003 is detectable for the entire range of reflectances and either for small blocks or the entire image.
    • for the blue band, as the variation of "Top of the Atmosphere" reflectance for the extreme conditions of atmospheric conditions (from 5 km to 23 km visibility) is about 0.035, differences of about 0.003 are detectable.

1-322 Radiometric calibration

    The radiometric calibration is specified in terms of:
  • Intra-image consistency :
    The calibration consistency within an entire image (large areas) give a NEdR better than 0.005 for any reflectance value.
  • Calibration accuracy :
    The calibration accuracy is comparable to the high resolution specifications that are within a quality range consistent with existing studies and probable needs for the next ten years:
    • interband and multitemporal calibration accuracy better than 3%,
    • absolute accuracy better than 5%.

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