Calibration of optical instruments



Radiometric calibration
.
Spectral-optical calibration
.
Collimator and manipulator
.
Camera-calibration laboratories

We can determine many properties of objects by measuring the optical radiation which will be reflected or emitted by these objects. Intensity and polarisation of the radiation and its spectral, spatial and temporal distribution carry the desired information. The measuring instruments produce digital data which combine the properties of the radiation and the properties of the instrument.

The calibration procedure delivers the parameter of an instrument in physical units. These parameter, for example wavelengtgh, FOV or response, effect the measured data and they are needed to deduce the properties of the object under investigation.

The calibration of an instrument is the basis for a scientific interpretation of the data and for the comparability of the results.

We in our department use and offer the following spectral-optical and radiometrical calibration equipment:

Spectral-optical measurements:

  • Monochromators using prisms and gratings, spectral and scientific lamps,
    spectral range: 400 ...1100 nm, spectral resolution: 0,1 nm;
    spectral range: 0,9 ...2,5 µm, spectral resolution: 1 nm

Radiation standards:

  • Spectral irradiance :
    1000W QTH lamps; spectral range of calibration 0,25...2,5 µm
    uncertainty of measurement < 5%
  • Spectral radiance:
    Integrating sphere of 500 mm diameter, port diameter: 200 mm, homogeneity > 98,5%, uncertainty of measurement < 5 %,
  • Diffuse spectral reflection:
    surfaces with diffuse reflection, Spectralon discs 60 mm, spectral range of calibration of the radiance coefficient ß(8°/d): 0,25...2,5 µm, different reflection coefficients (%): 2; 5; 10; 20; 40; 60; 80; 99; BaSO4 standard: 300 mm diameter, ß(0°/35°)


Instruments for measuring of spectral data:

  • Spectral photometer OL 750:
    spectral radiance and irradiance, spectral range: 0,28 ... 2,5 µm
  • Multichannel spectrometer BSF:
    spectral radiance and irradiance, spectral range: 13 channels from 400...1020 nm; spectral resolution: 10 nm, FOV: 18 * 26 mm²,
  • Spectrometer Lambda 19: Dual beam instrument for measuring the reflectivity and the transmissivity of optical materials: spectral range: 280…2500nm

Camera-calibration-facility

The camera-calibration-facility of the Department OS can be used for geometric, radiometric and spectral calibration of optoelectronical systems.

The following calibration.measurements can be done with high performance and precision:

  • Optimal adjusting and focussing of sensors
  • Determination of interior orientation any pixels (geometrical calibration)
  • Relative radiometric calibration-determination of PRNU und limb darkening
  • Absolut radiometric calibration by comparing with an integrating sphere
  • Geometric copixel-registration of sensors in vis-and IR-range.


Contact
Dr.rer.nat. Horst Schwarzer
German Aerospace Center

Institute of Optical Sensor Systems
, Optic, Calibration and Validation
Tel: +49 30 67055-584

Fax: +49 30 67055-572

E-Mail: Horst.Schwarzer@dlr.de
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