Gec Ferranti Defence Systems Limited

Bae Systems, Inc.

Selex Sensors and Airborne Systems Limited

Selex Galileo Limited

Norman Frederick Watson

Michael Grant McGuigan

A reference surface for calibrating cooled infra red detectors includes a plurality of corner cube units which reflect radiation incident directly on them. The surface of each corner cube unit is partially reflective and partially emissive such that, when imaged by a cryogenically cooled detector, the reference surface appears as a black body source at a lower temperature than the actual temperature thereof.

Calibration of infra red cameras

Described herein is a method and apparatus for calibrating an infrared camera at elevated temperatures using a reference surface. The method comprises selecting a normal well-fill condition for pixels in the camera in accordance with normal operating temperatures and stare time (), using the normal well-fill condition to calculate a selected stare time/surface temperature combination for which selected non-uniform calibration coefficients are determined (), adjusting and re-adjusting the stare time/surface temperature to obtain adjusted and re-adjusted non-uniform calibration coefficients respectively (), and determining final non-uniform calibration coefficients for the camera using the selected, adjusted and re-adjusted non-uniform calibration coefficients ().

Infra red camera calibration

A method for correcting an integral signal representing the integral of an input signal derived from an accelerometer to eliminate the effects of errors in the input signal comprises sampling one or more signals which bear a functional relationship with the errors and subjecting the samples to a correction algorithmic process. The processed results are integrated and used to correct the input signal integral. Relatively few samples may be taken at below the Nyquist rate at random or pseudorandom intervals to provide an acceptable quantitive estimate of the error in the integrated input signal. The samples are spaced throughout the integration period by defining window intervals and taking one or more samples randomly in each window interval. Apparatus to practice the method include an integrator for integrating the input signal and a sample and hold circuit for sampling the input signal. Sample signals are subjected to the correction algorithmic process under the control of a control circuit arranged to provide output control signals that define sampling intervals at a high frequency rate, sampling window intervals and the integration time. An accumulator receives and stores processed samples with the output of the accumulator applied to a correction circuit to correct errors in the input signal which after integration is also applied to the correction circuit, the output of the correction circuit representing the corrected signal.

Signal processing apparatus and method

A current-to-frequency converter 12' (FIG. 3) for use with an accelerometer 10 comprises a storage capacitor 13 which receives the accelerometer current and develops a charging voltage, reset charging means 25 which delivers timed charges to offset the voltage by predetermined amount and voltage sensing means 14' which senses the charging voltage reaching positive or negative thresholds in order to initiate a reset and offsetting the voltage. The polarity of charging voltage at which reset is triggered determines that polarity threshold as being half the magnitude of the offset voltage but the opposite polarity threshold of greater magnitude so that the voltage on the reset capacitor avoids it. If the acceleration current direction changes altering the charging voltage polarity the first reset at this high magnitude threshold existing for that polarity causes it to adopt the lower magnitude of half the reset offset voltage for subsequent resets and the opposite polarity adopt a threshold of the greater magnitude.

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Edinburgh, United Kingdom

Norman Frederick Watson