Minimize SCIAMACHY Product Handbook

Radiometric Calibration

Table of Contents

 

click to enlarge

fig. 4-5:

image
Definition of the coordinate frame used in the data processor for polarisation values q = Q/I, u = U/I. (graphics: DLR-IMF)
 

4.6 Radiometric Calibration


4.6 Radiometric Calibration

The final step in the calibration of the data is the radiometric calibration. The retrieval of trace gases usually uses the reflectance, the ratio of Earth radiance and solar irradiance. The solar irradiance is measured with on-board diffusers in-flight. The reflectance can be written as (equ. 4-9)

image

with image and image as the Earth and sun intensity and measured signal, image as the cosine of the solar zenith angle, image as the instrument radiometric response for limb (L) and nadir (N) and image as the instrument radiometric responses for sun diffuser measurements, as calculated from the Mueller matrix for the scanner and the polarisation sensitivity of the OBM. Because all matrix elements in equ. 4-9 relate to the detectors, we left the superscript ?D? out for better legibility. For a proper calibration the instrument responses have to be determined as a function of wavelength image and incidence angle image. All polarisation properties are calculated relative to the element of the polarisation sensitivity vectors, so the only remaining term needed for radiometric calibration is the image term which depends on image , image and image  for any limb, nadir or solar viewing geometry summarised here as:

image

where image identifies the first element in vector imageimage and image are provided in the calibration key data as determined from on-ground TV measurements, and image is calculated with the scanner model using as input the actual viewing geometry of the instrument, the complex index of refraction of the mirror material as determined during on-ground ambient calibration, and optionally any contamination built-up on the scan mirrors since launch.

 

Table of Contents
0 Attachments
2559 Views
Average (0 Votes)
The average rating is 0.0 stars out of 5.
Comments