Calibrating radiometers
First Claim
1. A method of improving the image quality of a multi-channel imaging radiometer having at least a first channel which detects radiation using a first detector and a second channel which detects radiation using a second detector, the method comprising modifying the gain and/or offset used in the scene-temperature vs detector voltage equations for the first and second channels using values for the gain and offset derived by performing a channel calibration operation, and in that channel calibration operation ensuring that the first and second channels observe substantially the same temperature and using the outputs from the first and second detectors in the calibration operation to produce a modified value for the gain and/or offset for the first and/or second channel;
- the radiometer using the modified gain and/or offset for the first and/or second channel to create an image using the first and second channels.
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Accused Products
Abstract
Radiometers detect radio wavelength electromagnetic radiation and typically have an antenna (16), an amplifier (18) and a detector (20). All three of these components have response characteristics that may be dependent on temperature, and in the case of systems using radiometer arrays dependent upon temperatures throughout the system. Different temperatures across a multi-channel antenna and differential channel temperature response can result in poor image quality from imaging radiometers. Resolution of a linear array of detector horns is limited by the size of the horns. An imaging radiometer (10) uses a focussing polariser (36), a quarter wave plate (32), a rotating inclined disk (28), and a detector feed array (16) to perform a conical scan, and compensates for variations in operating temperature of a radiometer using one or more of a variety of techniques including calibrating channels relative to each other, calibrating channels using reference temperatures in situo, and calibrating channels using temperature response predictions stored in the radiometer signal processor (22). Aspects of the invention also optimise image resolution, image quality and allow calibration.
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Citations
39 Claims
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1. A method of improving the image quality of a multi-channel imaging radiometer having at least a first channel which detects radiation using a first detector and a second channel which detects radiation using a second detector, the method comprising modifying the gain and/or offset used in the scene-temperature vs detector voltage equations for the first and second channels using values for the gain and offset derived by performing a channel calibration operation, and in that channel calibration operation ensuring that the first and second channels observe substantially the same temperature and using the outputs from the first and second detectors in the calibration operation to produce a modified value for the gain and/or offset for the first and/or second channel;
- the radiometer using the modified gain and/or offset for the first and/or second channel to create an image using the first and second channels.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 39)
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15. A multi-channel imaging radiometer having a first channel having a first channel detector and being adapted to be connected to a first channel observed scene radiation capturer, and a second channel having a second channel detector and being adapted to be connected to a second channel observed scene radiation capturer, and a signal processor, in which observed scene radiation signals are adapted to be fed to the first and second detectors respectively by their first and second channels, and the detectors are adapted in use to provide first and second detector outputs to the signal processor, the signal processor being adapted in use to provide output signals representative of the temperatures observed in the observed scene by the first and second channels;
- and in which the signal processor is adapted in use to operate on the received first and second detector outputs using values representative of, influenced by, or associated with the gain and voltage offset for the first channel and for the second channel to calibrate the gain and voltage offset for the second channel relative to those of the first channel.
- View Dependent Claims (16, 17, 18, 19, 20)
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21. A method of improving the accuracy of an image or of output signals image produced by a radiometer comprising the steps of:
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periodically performing an absolute calibration step, the absolute calibration step comprising exposing at least one radiation detection channel to a source of known temperature, wherein said known temperature comprises the sky; and
adjusting one of gain and offset voltage of said at least one radiation detection channel to an absolute calibration function. - View Dependent Claims (22, 23)
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- 24. A radiometer having at least one detection channel and a detector adapted to receive radiation acquired in use by the channel, a control processor, and an absolute reference temperature provider, the arrangement being such that the radiometer can be put, in use, in a calibration mode in which it resets the gain and/or offset associated with the, at least one, or each, channel by using signals derived from the reference temperature provider.
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28. A method of improving the performance of a radiometer having at least one detection channel comprising the steps of;
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evaluating a scene temperature; and
using an equivalence function in response to said evaluated scene temperature, providing compensation for variations in temperature of at least one component of the radiometer. - View Dependent Claims (29, 30, 31, 32)
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- 33. A method of calibrating a radiometer having a detector channel having a detector feed and a detector, and a scanner which scans an observed scene by directing different parts of the scene onto the detector feed of the detector channel at different times, with each notional pixel in an observed scene observed by the channel having an associated scan angle, the method comprising modifying the observed scene temperature detected by the detector by one of a calibration and compensation function which is dependant upon the scan angle of the notional pixel being observed and is independent of the orientation of the radiometer relative to the observed scene.
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37. A scanning imaging radiometer comprising:
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a scanner for scanning notional pixels in an observed scene onto a detector element of a detector channel, and a control processor for receiving signals from the detector element and for evaluating the scene temperature of the notional pixel from the output of the detector element and, from one of a concordance and algorithm, compensating for the scan angle at which the pixel was evaluated independent of the orientation of the radiometer relative to the observed scene. - View Dependent Claims (38)
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Specification