PASSIVE RANGEFINDER

Abstract

A passive rangefinder for determining the range to an object such as an aircraft, rocket or missile which emits electromagnetic radiation makes use of spectral measurements over a broad band of frequencies. The rangefinder includes means 202 for forming a real image of a field of view, spectrophotometer means 201 including an entrance aperture 27 placed to receive at least a part of said real image, dispersion means (15, 28, 29) for separating radiation of different wavelengths and detector means 24 for measuring the spectrum of radiation received from distinct portions of the entrance aperture. The detector output is connected to data processing means 204 arranged to deconvolve the received spectral profile with a stored representation (205) of a range-dependent atmospheric transmission spectral profile to obtain a representation of the spectral emission profile of radiation from the object. From the emission spectral profile a characteristic temperature of emission (206) is derived and hence a Planck emission spectrum for the object. The Planck spectrum is used to determine the range from the calculated emission spectrum and the observed spectrum (205, 208). Thus by deconvolving the measured spectrum with the atmospheric transmission spectrum the range can be determined. The invention can work at any range of e.m. radiation for which suitable components are available. Advantageously the ranging is done on two different temperature portions of the same object so that different Planck profiles are used in the signal processing. The atmospheric transmission spectrum can be measured prior to operation in the prevailing conditions by use of a laser rangefinder.

Source: Google Patents

35 USC §181 Secrecy Order

Inventor

• 1HERBERT A. FRENCH

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