Dr. Evangelos Theocharous Profile

Dr. Evangelos Theocharous

Manager/Special Projects at National Physical Lab

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Publications (8)

Proceedings Article | 5 September 2017 Presentation + Paper

The EarthCARE mission BBR instrument: ground testing of radiometric performance

Martin Caldwell, David Spilling, William Grainger, E. Theocharous, Martin Whalley, Nigel Wright, Anthony Ward, Edward Jones, Joseph Hampton, David Parker, John Delderfield, Alan Pearce, Tony Richards, Grant Munro, Oliver Poynz Wright, Matthew Hampson, David Forster

Proceedings Volume 10402, 1040204 (2017) https://doi.org/10.1117/12.2273148

KEYWORDS: Calibration, Radiometry, Solar radiation, Aerosols, LIDAR, Clouds, Radar, Imaging systems, Sensors, Optical filters

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In the EarthCARE mission the BBR (Broad Band Radiometer) has the role of measuring the net earth radiance (i.e. total reflected-solar and thermally-emitted radiances), from the same earth scene as viewed by the other instruments (aerosol lidar, cloud radar and spectral imager). It does this measurement at 10km scene size and in 3 view angles. It is an imaging radiometer in that it uses micro-bolometer linear-array detector (pushbroom orientation), to over-sample these required scenes, with the samples being binned on-ground to produce the 10km radiance data. For the measurements of total earth radiance, the BBR is based on the heritage of Earth Radiation Budget (ERB) instruments. The ground calibration methods of this type of sensor is technically very similar to other EO instruments that measure in the thermalIR, but with added challenges: (1) The thermal-IR measurement has to have a much wider spectral range than normal thermal-IR channels to cover the whole earth-emission spectrum i.e. ~4 to >50microns; (2) The 2nd channel (reflected solar radiance) must also have a broad response to cover almost the whole solar spectrum, i.e. ~0.3 to 4microns. And this solar channel must be measured on the same radiometric calibration as the thermal channel, which in practice is best done by using the same radiometer for both channels. The radiometer is designed to be very broad-band i.e. 0.3 to 50microns (i.e. more than two decades), to cover both ranges, and a switchable spectral filter (short-pass cutoff at 4μm) is used to separate the channels. The on-ground measurements which are required to link the calibration of these channels will be described. A calibration of absolute responsivity in each of the two bands is needed; in the thermal-IR channel this is by the normal method of using a calibrated blackbody test source, and in the solar channel it is by means of a narrow-band (laser) and a reference radiometer (from NPL). A calibration of relative spectral response is also needed, across this wide range, for the purpose of linking the two channels, and for converting the narrow-band solar channel measurement to broad-band.

Proceedings Article | 28 April 2010 Paper

Characterisation of photon counting systems at NPL

Evangelos Theocharous, Jessica Cheung, Christopher Chunnilall

Proceedings Volume 7681, 768105 (2010) https://doi.org/10.1117/12.851861

KEYWORDS: Photon counting, Sensors, Nanolithography, Photodetectors, Silicon, Indium gallium arsenide, Calibration, Signal detection, Optical metrology, Photodiodes

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Proceedings Article | 12 April 2004 Paper

The NPL wide-area MIR calibration source

Martin Dury, Evangelos Theo Theocharous, Neil Harrison, Moira Hilton, Nigel Fox

Proceedings Volume 5405, (2004) https://doi.org/10.1117/12.563841

KEYWORDS: Black bodies, Nanolithography, Coating, Reflectivity, Copper, Calibration, Temperature metrology, Monte Carlo methods, Reflectors, Mid-IR

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Proceedings Article | 8 December 2003 Paper

Development and evaluation of a novel large-area single-pixel QWIP for infrared radiometry

Leon Rogers, Evangelos Theocharous, Juntaro Ishii, Nigel Fox

Proceedings Volume 5209, (2003) https://doi.org/10.1117/12.508787

KEYWORDS: Sensors, Quantum well infrared photodetectors, Infrared radiation, Thermography, Infrared detectors, Radiometry, Infrared sensors, Mercury cadmium telluride, Nanolithography, Polarization

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Proceedings Article | 8 December 2003 Paper

Latest measurement techniques at NPL for the characterization of infrared detectors and materials

Evangelos Theocharous, Frank Clarke, Leon Rogers, Nigel Fox

Proceedings Volume 5209, (2003) https://doi.org/10.1117/12.509482

KEYWORDS: Sensors, Nanolithography, Reflectivity, Calibration, Mirrors, Infrared detectors, Transmittance, Reflectometry, Monochromators, Infrared radiation

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Proceedings Article | 8 August 2003 Paper

Wavelength-tunable quasi-cw laser source for high-accuracy spectrometric measurement in the 200-nm to 500-nm region

William Hartree, Evangelos Theocharous, Nigel Fox

Proceedings Volume 4826, (2003) https://doi.org/10.1117/12.514530

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Proceedings Article | 8 November 1996 Paper

Comparison of the performance of infrared detectors for radiometric applications

Evangelos Theocharous, Nigel Fox, Tim Prior

Proceedings Volume 2815, (1996) https://doi.org/10.1117/12.257159

KEYWORDS: Sensors, Infrared detectors, Photoresistors, Infrared radiation, Infrared sensors, Resistance, Standards development, Radiometry, Indium gallium arsenide, Germanium

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Proceedings Article | 30 May 1995 Paper

Radiometric calibration of infrared detectors and thermal imaging systems

Nigel Fox, Tim Prior, Evangelos Theocharous

Proceedings Volume 2474, (1995) https://doi.org/10.1117/12.210558

KEYWORDS: Sensors, Calibration, Thermography, Infrared detectors, Imaging systems, Infrared radiation, Nanolithography, Monochromators, Temperature metrology, Infrared sensors

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Showing 5 of 8 publications

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