The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
C S Ruf - One of the best experts on this subject based on the ideXlab platform.
-
inter calibration of microwave Radiometers using the vicarious cold calibration double difference method
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2012Co-Authors: Rachael Kroodsma, Darren Mckague, C S RufAbstract:The double difference method of inter-calibration between spaceborne microwave Radiometers is combined with the vicarious cold calibration method for calibrating an individual radiometer. Vicarious cold calibration minimizes the effects of geophysical variability on radiative transfer models (RTMs) of the brightness temperature (TB) data and it accounts for frequency and incidence angle dissimilarity between Radiometers. Double differencing reduces the sensitivity of the inter-calibration to RTM error and improper accounting for geophysical variables in the RTM. When combined together, the two methods significantly improve the confidence with which calibration differences can be identified and characterized. This paper analyzes the performance of the vicarious cold calibration double difference method for conical scanning microwave Radiometers and quantifies the improvement this method provides compared to performing a simpler inter-calibration by direct comparison of radiometer measurements.
-
detection of calibration drifts in spaceborne microwave Radiometers using a vicarious cold reference
IEEE Transactions on Geoscience and Remote Sensing, 2000Co-Authors: C S RufAbstract:The coldest possible brightness temperatures observed by a downward-looking microwave radiometer from space are often produced by calm oceans under cloud-free skies and very low humidity. This set of conditions tends to occur with sufficient regularity that an orbiting radiometer will accumulate a useful number of observations within a period of a few days to weeks. Histograms of the radiometer's coldest measurements provide an anchor point against which very small drifts in absolute calibration can be detected. This technique is applied to the TOPEX microwave radiometer (TMR), and a statistically significant drift of several tenths of a Kelvin per year is clearly detected in one of the channels. TMR housekeeping calibration data indicates a likely cause for the drift, as small changes in the isolation of latching ferrite circulators that are used in the onboard calibration-switch assembly. This method can easily be adapted to other microwave Radiometers, especially imagers operating at frequencies in the atmospheric windows. In addition to detecting long-term instrument drifts with high precision, the method also provides a means for cross-calibrating different instruments. The cold reference provides a common tie point, even between sensors operating at different polarizations and/or incidence angles.
Stephen D. Pye - One of the best experts on this subject based on the ideXlab platform.
-
A study of the directional response of ultraviolet Radiometers: II. Implications for ultraviolet phototherapy derived from computer simulations
Physics in medicine and biology, 2000Co-Authors: Colin J Martin, Stephen D. PyeAbstract:A theoretical model has been used to simulate irradiances for ultraviolet (UV) phototherapy cabinets and other sources. The accuracy of the simulation results has been checked by comparison with experimental measurements. The simulations have been used to study the influence of different factors on UV phototherapy exposure and to develop recommendations for the operation and calibration of phototherapy cabinets. Many Radiometers used in the evaluation of skin doses have input optics with directional responses that are not proportional to the cosine of the angle of incidence for the UV radiation. Data on radiometer directional responses have been incorporated into the simulations, which show that the poor directional responses for some Radiometers currently in use will give errors of 20-50% in the assessment of irradiance. The influence of lamp source geometries employed for radiometer calibration has been investigated. UV phototherapy dosimetry commonly uses a spectroradiometer and a radiometer in the transfer of irradiance calibrations from a small standard UV lamp to a large-area source with a different UV spectrum. Recommendations are given on the range of acceptability for radiometer directional responses and a method is described for determining whether these are fulfilled. Recommendations are made on the techniques that should be used for calibration.
-
The importance of radiometer angular response for ultraviolet phototherapy dosimetry.
Physics in medicine and biology, 1999Co-Authors: Colin J Martin, G D Currie, Stephen D. PyeAbstract:The influence of the angular response of radiometer probes on measurements of irradiance in ultraviolet phototherapy has been studied. Irradiance measurements were made using nine ultraviolet (UV) Radiometers employed by phototherapy centres in Scotland and Northern Ireland, and compared with measurements made using two spectroRadiometers. The light sources used were UVB TL01 fluorescent lamps, arranged in different geometries. Irradiances within TL01 whole body treatment cabinets were assessed based on a comparison with one of the spectroRadiometers. The results show variations of 50% in cabinet irradiance measurements made by different Radiometers, even when they were calibrated using the same source geometry and spectroradiometer. Differences in radiometer probe design and construction lead to an under- or over-response at angles of incidence greater than zero. Angular responses of different probes were assessed using banks of fluorescent lamps. The differences found are large enough to account for the variations in measurements of cabinet irradiance. The variations in irradiance measurements are significant in terms of planning and monitoring patient exposure during TL01 phototherapy. Accurate dosimetry can only be achieved if radiometer probes have a good cosine response and recommendations are made for better calibration techniques.
Lyma A Page - One of the best experts on this subject based on the ideXlab platform.
-
first year wilkinson microwave anisotropy probe wmap observations on orbit radiometer characterization
Astrophysical Journal Supplement Series, 2003Co-Authors: N Jarosik, C Arnes, C L Enne, M Halpe, Gary Hinshaw, A Kogu, M Limo, S S Meye, Lyma A PageAbstract:The WMAP satellite has completed 1 year of measurements of the cosmic microwave background (CMB) radiation using 20 differential high electron mobility transistor (HEMT) based Radiometers. All the Radiometers are functioning nominally, and characterizations of the on-orbit radiometer performance are presented, with an emphasis on properties that are required for the production of sky maps from the time-ordered data. A radiometer gain model, used to smooth and interpolate the CMB dipole gain measurements, is also presented. No degradation in the sensitivity of any of the Radiometers has been observed during the first year of observations.
-
first year wilkinson microwave anisotropy probe wmap observations on orbit radiometer characterization
arXiv: Astrophysics, 2003Co-Authors: N Jarosik, Gary Hinshaw, Lyma A Page, Cris W Barnes, C L Bennett, M Halpern, A Kogut, M Limon, S S Meyer, David N SpergelAbstract:The WMAP satellite has completed one year of measurements of the Cosmic Microwave Background (CMB) radiation using 20 differential high-electron-mobility-transistor (HEMT) based Radiometers. All the Radiometers are functioning nominally, and characterizations of the on-orbit radiometer performance are presented, with an emphasis on properties that are required for the production of sky maps from the time ordered data. A radiometer gain model, used to smooth and interpolate the CMB dipole gain measurements is also presented. No degradation in the sensitivity of any of the Radiometers has been observed during the first year of observations.
Colin J Martin - One of the best experts on this subject based on the ideXlab platform.
-
A study of the directional response of ultraviolet Radiometers: II. Implications for ultraviolet phototherapy derived from computer simulations
Physics in medicine and biology, 2000Co-Authors: Colin J Martin, Stephen D. PyeAbstract:A theoretical model has been used to simulate irradiances for ultraviolet (UV) phototherapy cabinets and other sources. The accuracy of the simulation results has been checked by comparison with experimental measurements. The simulations have been used to study the influence of different factors on UV phototherapy exposure and to develop recommendations for the operation and calibration of phototherapy cabinets. Many Radiometers used in the evaluation of skin doses have input optics with directional responses that are not proportional to the cosine of the angle of incidence for the UV radiation. Data on radiometer directional responses have been incorporated into the simulations, which show that the poor directional responses for some Radiometers currently in use will give errors of 20-50% in the assessment of irradiance. The influence of lamp source geometries employed for radiometer calibration has been investigated. UV phototherapy dosimetry commonly uses a spectroradiometer and a radiometer in the transfer of irradiance calibrations from a small standard UV lamp to a large-area source with a different UV spectrum. Recommendations are given on the range of acceptability for radiometer directional responses and a method is described for determining whether these are fulfilled. Recommendations are made on the techniques that should be used for calibration.
-
The importance of radiometer angular response for ultraviolet phototherapy dosimetry.
Physics in medicine and biology, 1999Co-Authors: Colin J Martin, G D Currie, Stephen D. PyeAbstract:The influence of the angular response of radiometer probes on measurements of irradiance in ultraviolet phototherapy has been studied. Irradiance measurements were made using nine ultraviolet (UV) Radiometers employed by phototherapy centres in Scotland and Northern Ireland, and compared with measurements made using two spectroRadiometers. The light sources used were UVB TL01 fluorescent lamps, arranged in different geometries. Irradiances within TL01 whole body treatment cabinets were assessed based on a comparison with one of the spectroRadiometers. The results show variations of 50% in cabinet irradiance measurements made by different Radiometers, even when they were calibrated using the same source geometry and spectroradiometer. Differences in radiometer probe design and construction lead to an under- or over-response at angles of incidence greater than zero. Angular responses of different probes were assessed using banks of fluorescent lamps. The differences found are large enough to account for the variations in measurements of cabinet irradiance. The variations in irradiance measurements are significant in terms of planning and monitoring patient exposure during TL01 phototherapy. Accurate dosimetry can only be achieved if radiometer probes have a good cosine response and recommendations are made for better calibration techniques.
M Limo - One of the best experts on this subject based on the ideXlab platform.
-
first year wilkinson microwave anisotropy probe wmap observations on orbit radiometer characterization
Astrophysical Journal Supplement Series, 2003Co-Authors: N Jarosik, C Arnes, C L Enne, M Halpe, Gary Hinshaw, A Kogu, M Limo, S S Meye, Lyma A PageAbstract:The WMAP satellite has completed 1 year of measurements of the cosmic microwave background (CMB) radiation using 20 differential high electron mobility transistor (HEMT) based Radiometers. All the Radiometers are functioning nominally, and characterizations of the on-orbit radiometer performance are presented, with an emphasis on properties that are required for the production of sky maps from the time-ordered data. A radiometer gain model, used to smooth and interpolate the CMB dipole gain measurements, is also presented. No degradation in the sensitivity of any of the Radiometers has been observed during the first year of observations.
