US 5,311,273 AGranted

Method and apparatus for calibrating spectral radiometers

AssigneeDeutsche Forschungsanstalt fur Luft- und Raumfahrt e.V.

InventorsVolker Tank, Peter Haschberger, Helmut Dietl, Erwin Lindermeier

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Abstract

A method and an apparatus are provided for calibrating a spectrometer, in particular a Fourier transform spectrometer (FTS), in particular for the infrared spectral range. At least four black body radiators of different temperatures are provided, which are arranged horizontally, i.e. parallel to the surface of the earth, thereby avoiding temperature gradients due to convection. The temperature of the at least four radiators is determined by means of the calibrating method without a separate measurement. In the method according to the invention, at the same time the absorption of the atmosphere is considered as a characteristic of the spectrometer, thereby eliminating separate measurement and correction thereof. In addition, for Fourier transform spectrometers the calibration is carried out by means of complex spectra.

Claims9

Dependent claims

A method for calibrating spectral radiometers, with the aid of black body radiators, wherein

from measured spectra of at least four black radiators (1.sub.1 to 1.sub.4) aligned parallel to the surface of the earth and held constant at respective different temperatures four different groups of different spectra of three radiators (1.sub.1, 1.sub.2, 1.sub.3 ;
1.sub.2, 1.sub.3, 1.sub.4 ;
1.sub.3, 1.sub.4, 1.sub.1 and 1.sub.4, 1.sub.1, 1.sub.2 in each case are formed;
from each of the four different groups of different spectra by a least square fit the spectral sensitivity (R(.nu..sub.i)), the spectral inherent radiation from the apparatus (G(.nu..sub.i)) and the respective three radiator temperatures (T.sub.h) are determined, and
in the presence of the spectra of n(n>3) wave numbers (.nu.) the results of the four groups each of three different spectra are compared with each other, a calibration being considered reliable when the results for the spectral sensitivity (R(.nu..sub.i)) and the spectral inherent radiation (G(.nu..sub.i)) and the four different radiator temperatures (T.sub.h) coincide in the order of magnitude of the measuring inaccuracy of the spectrometer.

2 more elements

An apparatus for calibrating spectral radiometers, with the aid of black body radiators, wherein at least four circular black body radiators (1.sub.1 to 1.sub.4) held constant at different temperatures (T.sub.h) and arranged parallel to the surface of the earth so that they emit their radiation upwardly can be consecutively positioned beneath a stationary plane mirror (5), the mirror surface of which encloses an angle of 45.degree. both with the radiator surfaces and with the aperture opening of the spectrometer (6) to be calibrated, the surface of the plane mirror (5) being so dimensioned that it is greater than the projection onto the radiator surfaces, and the area of the radiators (1.sub.1 to 1.sub.4) again covering the circular aperture area of the spectrometer (6) to be calibrated so that the radiation of each of the positioned black body radiators is reflected into the optical system of the spectrometer to be calibrated.

Dependencies are inferred from the claim text.