1. Sensor calibration

2. Why is sensor calibration important?
Sensors drift over time and this results in uncertainties
To deduce accurate information from imaging spectroscopy data

3. Calibration categories
3 types of calibration categories
Lab calibration
In-flight calibration
Vicarious calibration

4. Lab calibration Ideally before and after each mission
Seismic block
7 m
6 m
12 m
Lab calibration
Ideally before and after each mission
In practice before and after flight season
Labour and cost intensive (especially for pushbroom sensors)
Low humidity and T-controlled circumstances
Calibration on seismic block

5. Lab calibration (cont’d)
3 types of lab calibration
Geometric
Spectral
Radiometric

6. Geometric calibration
To determine the spatial response function of each detector element
Using e.g. high precision tilt stage to direct a collimated beam into the FOV and scanning the spatial response for each detector element across track

7. Lab calibration (cont’d)
3 types of lab calibration
Geometric
Spectral
Radiometric

8. Spectral calibration
To determine the centre wavelength and width of the spectral response function of each detector element (row)
Row to wavelenght is a linear function
Using a wavelenght standard (e.g. Mylar) with discrete emission or absorption features or a monochromator (expensive!)

9. Lab calibration (cont’d)
3 types of lab calibration
Geometric
Spectral
Radiometric

10. Radiometric calibration
To convert DN to radiance
Using a radiance standard (e.g. integrating sphere) with known radiance which is
Stable
Uniform
Lambertian

11. Radiometric calibration (cont’d)
ADS
Integrating
Sphere
Field Spectrometer with Fiber Optics
FOV
QTH Lamps for various
radiance levels
APEX
Ø1,60 m

12. Radiometric calibration (cont’d)
Known radiance of the standard is compared to the detector response (DN) after spectral calibration and dark signal subtraction
Linear function assumed

13. Calibration categories
3 types of calibration categories
Lab calibration
In-flight calibration
Vicarious calibration

14. In-flight calibration
Operational conditions differ from lab conditions
Not a full calibration but a check of the lab calibration using an on-board lamp during operation
Less labour and cost intensive than lab calibration
Before and after data acquisition

15. Calibration categories
3 types of calibration categories
Lab calibration
In-flight calibration
Vicarious calibration

16. Vicarious calibration
Means to validate the sensor’s performance
By simultaneous data acquisition and in-situ measurements of stable, homogeneous, Lambertian targets
Atmospheric input parameters required to link airborne/spaceborne data with in-situ data