Showing papers on "Radiometer published in 2000"
TL;DR: The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a high spatial resolution, multispectral imager with along-track stereo capabilities scheduled for launch on the first NASA spacecraft of the Earth Observing System (Terra) in 1999 as discussed by the authors.
Abstract: The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a high spatial resolution, multispectral imager with along-track stereo capabilities scheduled for launch on the first NASA spacecraft of the Earth Observing System (Terra) in 1999. Data will be obtained in 14 spectral bands covering the visible through the thermal infrared wavelength region. A number of standard data products will be available to requesters through an on-line archival and processing system. Particular, user-specified data acquisitions will be possible through a Data Acquisition Request system.
568 citations
TL;DR: First a data-simulation approach is taken to isolate and analyze those influential factors in the calibration process and effective techniques are developed to reduce calibration uncertainties, and these techniques are applied to experimental data.
Abstract: The tipping-curve calibration method has been an important calibration technique for ground-based microwave radiometers that measure atmospheric emission at low optical depth. The method calibrates a radiometer system using data taken by the radiometer at two or more viewing angles in the atmosphere. In this method, the relationship between atmospheric opacity and viewing angle is used as a constraint for deriving the system calibration response. Because this method couples the system with radiative transfer theory and atmospheric conditions, evaluations of its performance have been difficult. In this paper, first a data-simulation approach is taken to isolate and analyze those influential factors in the calibration process and effective techniques are developed to reduce calibration uncertainties. Then, these techniques are applied to experimental data. The influential factors include radiometer antenna beam width, radiometer pointing error, mean radiating temperature error, and horizontal inhomogeneity in the atmosphere, as well as some other factors of minor importance. It is demonstrated that calibration uncertainties from these error sources can be large and unacceptable. Fortunately, it was found that by using the techniques reported, the calibration uncertainties can be largely reduced or avoided. With the suggested corrections, the tipping calibration method can provide absolute accuracy of about or better than 0.5 K.
209 citations
TL;DR: In this paper, a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 21 years, and the corrections which are needed for each radiometer, mainly to compensate for degradation, but also for operational influences are described.
Abstract: Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 21 years. From measurements made by different space radiometers (HF on NIMBUS-7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. The corrections which are needed for each radiometer, mainly to compensate for degradation, but also for operational influences are described. ACRIM I (1980–1989) and ACRIM II (1992–1995) are taken as reference because their degradation was monitored by inflight comparisons with spare radiometers; since 1996 VIRGO is used as reference. The scale of ACRIM II is adjusted to ACRIM I by comparison with NIMBUS-7 and ERBE. The reliability of this adjustment depends strongly on the stability of the HF and ERBE radiometer during the period of the gap between the ACRIMs which is discussed in detail together with an assessment of the overall precision of the composite.
174 citations
TL;DR: In this article, an L-band 2-D microwave interferometric radiometer for monitoring surface variables over land surfaces is discussed. But the authors focus on the retrieval capabilities of the satellite for monitoring soil moisture, vegetation biomass, and surface temperature.
164 citations
TL;DR: Mapping of Loki in I24 shows uniform temperatures for most of Loki Patera and high temperatures in the southwest corner, probably resulting from an eruption that began 1 month before the observation.
Abstract: Galileo's photopolarimeter-radiometer instrument mapped Io's thermal emission during the I24, I25, and I27 flybys with a spatial resolution of 2.2 to 300 kilometers. Mapping of Loki in I24 shows uniform temperatures for most of Loki Patera and high temperatures in the southwest corner, probably resulting from an eruption that began 1 month before the observation. Most of Loki Patera was resurfaced before I27. Pele's caldera floor has a low temperature of 160 kelvin, whereas flows at Pillan and Zamama have temperatures of up to 200 kelvin. Global maps of nighttime temperatures provide a means for estimating global heat flow.
134 citations
TL;DR: 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.
Abstract: 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.
120 citations
TL;DR: In this article, the microwave radiance emanating from ice clouds at arbitrary viewing angles is expressed as an analytic function of the cloud ice water path (IWP), the particle effective diameter (De), and the particle bulk density (ρi).
Abstract: Based on the radiative transfer theory, the microwave radiance emanating from ice clouds at arbitrary viewing angles is expressed as an analytic function of the cloud ice water path (IWP), the particle effective diameter (De), and the particle bulk density (ρi). Thus, for a given particle density, the earth-viewing measurements at two frequencies (e.g., 340 and 89 GHz) can provide an estimate of De and IWP for submillimeter-size particles. This physical retrieval is tested using data from the Millimeter-wave Imaging Radiometer (MIR). A comparison among MIR, radar, and infrared sensor measurements shows that the MIR frequencies are affected primarily by thick ice clouds such as cirrus anvil and convection. Over highly convective areas, the measurements from 89 to 220 GHz are nearly identical since the scattering by large ice particles aloft approaches the geometric optics limit, which is independent of wavelength. Under these conditions, only the lower MIR frequencies (89 and 150 GHz) are used to ...
118 citations
TL;DR: Use of NASA scatterometer (NSCAT) data, European remote sensing (ERS) advanced microwave instrument (AMI) scatterometer mode data, and special sensor microwave/imager (SSM/I) data to study surface roughness effects in Antarctica are explored.
Abstract: While designed for ocean observation, scatterometer and radiometer data have proven very useful in a variety of cryosphere studies. Over large regions of Antarctica, ice sheet and bedrock topography and the snow deposition, drift, and erosional environment combine to produce roughness on various scales. Roughness ranges from broad, basin-scale ice-sheet topography at /spl sim/100 km wavelengths to large, spatially coherent dune fields at /spl sim/10 km wavelength to erosional features on the meter scale known as sastrugi. These roughness scales influence the microwave backscattering and emission properties of the surface, combining to introduce azimuth-angle dependencies in the satellite observation data. In this paper, the authors explore the use of NASA scatterometer (NSCAT) data, European remote sensing (ERS) advanced microwave instrument (AMI) scatterometer mode data, and special sensor microwave/imager (SSM/I) data to study surface roughness effects in Antarctica. All three sensors provide strong evidence of azimuth modulation, which is correlated with the surface slope environment and results in a katabatic wind flow regime. Due to its broad azimuth coverage, NSCAT data appears to be the best suited for azimuth-angle observations. A simple empirical model for the azimuth variation in the radar backscatter is developed, and an algorithm for computing the parameters of the model from NSCAT data at a fine scale is presented. Results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small-scale roughness relative to the sensor-look direction.
105 citations
TL;DR: In this paper, global distributions of the aerosol optical thickness and Angstrom exponent were estimated from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer channel-1 and -2 radiances for four months in 1990.
Abstract: Global distributions of the aerosol optical thickness and Angstrom exponent are estimated from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer channel-1 and -2 radiances for four months in 1990. Global distributions of those Angstrom parameters are consistent with present knowledge on the distributions of desert-derived, biomass-burning, and anthropogenic pollutant aerosols obtained by ground- based and aircraft measurements. Especially, it is found that thin anthropogenic aerosols can be identified with large Angstrom exponent values around the east coast of North America, Europe, and eastern Asia. Satellite- retrieved values of Angstrom parameters are further compared with measured spectral optical thickness obtained by the National Aeronautics and Space Administration Aerosol Robotic Network sky radiometer network.
99 citations
TL;DR: In this article, the Physikalisch-Technische Bundesanstalt has further improved and extended its spectral responsivity scale based on the laser-operated radiation thermometry cryogenic radiometer.
Abstract: The Physikalisch-Technische Bundesanstalt has further improved and extended its spectral responsivity scale based on the laser-operated radiation thermometry cryogenic radiometer. Five laser wavelengths in the ultraviolet (UV) (238 nm to 400 nm) and another fifteen in the visible and near-infrared (NIR) (400 nm to 1015 nm) almost cover the entire spectral range where silicon photodiodes can be used in air. The lasers employed are a Kr+ laser, an Ar+ laser with optional intra-cavity frequency-doubling, and a continuously tuneable Ti:sapphire ring laser. The total relative standard uncertainty of the spectral responsivity at the laser lines is u = 10-4 in the visible and NIR below 950 nm and u = 10-3 in the UV. With an improved model for interpolation between the laser wavelengths, a continuous scale of spectral responsivity has been established in the wavelength range 400 nm to 1015 nm.
92 citations
TL;DR: The results of this paper show that the proposed technique is feasible, that it is expected to provide a good estimate of the temperature profile within the cooled baby-head, and that the estimated precision of theTemperature measured in the deep brain structures is better than 0.8 K, depending upon the estimation procedure used.
Abstract: Clinical studies of hypothermal neural rescue therapy for newborn infants who have suffered hypoxia-ischaemia are currently hindered by the difficulty in measuring deep brain temperature. This paper addresses: the specific requirements for this measurement problem, the design of a proposed radiometer system, a method for retrieving the temperature profile within the cooled head, and an estimation of the precision of the measurement of deep brain temperature using the technique. A five-frequency-band radiometer with a contact-type antenna operating within the range 1-4 GHz is proposed to obtain brightness temperatures corresponding to temperature profiles predicted by a realistic thermal model of the cooled baby head. The problems of retrieving the temperature profile from this set of brightness temperatures, and the estimation of its precision, are solved using a combination of model fitting and Monte Carlo techniques. The results of this paper show that the proposed technique is feasible, that it is expected to provide a good estimate of the temperature profile within the cooled baby-head, and that the estimated precision (2/spl sigma/) of the temperature measured in the deep brain structures is better than 0.8 K, depending upon the estimation procedure used.
TL;DR: In this article, two aerosol optical depth retrieval algorithms, using different instruments and different methods, are compared, using data from the ERS-2 overpass over northwestern Europe on 25 July 1995.
TL;DR: In this paper, a spectral calibration facility based on a calibrated trap detector from the Physikalisch-Technische Bundesanstalt (PTB, Germany) is used to relate the filter radiometer to an accurate and long-term traceable standard.
Abstract: Atmospheric optical depths are determined by relating ground-based measurements of direct solar radiation to the extraterrestrial value, I0, that a filter radiometer would read outside the atmosphere. Usually I0 is determined by the Langley extrapolation technique from a high-altitude site, where clear and highly stable atmospheric conditions may be found. Alternatively, I0 can be measured in situ from a stratospheric balloon experiment. We have employed both methods and found agreement to better than 1 %. Filter radiometers tend to change over time, especially when used operationally outdoors. Absolute calibrations in the laboratory are used to monitor the radiometric stability of filter radiometers at the Physikalisch-Meteorologisches Observatorium Davos (PMOD/WRC, Switzerland). A spectral calibration facility based on a calibrated trap detector from the Physikalisch-Technische Bundesanstalt (PTB, Germany) is used to relate the filter radiometer to an accurate and long-term traceable standard. An FEL-lamp-based standard, previously used for several years, was compared with the new trap standard via a filter radiometer at four wavelengths between 368 nm and 862 nm and revealed a systematic difference of the order of 5 %. The link between radiometric and I0 calibration is the value of the extraterrestrial solar spectrum at the filter radiometer wavelengths which can be determined from these two calibrations and compared with published values.
TL;DR: Comparisons with path delays derived from the special sensor microwave imager (SSM/I) instruments and a network of 15 island radiosondes provide consistent evidence that the TMR path delay measurements included an instrument-related downward drift.
Abstract: The stability and accuracy of the TOPEX Microwave Radiometer (TMR) measurement of the atmospheric path delay due to water vapor is assessed over the interval from launch (August 1992) through June 1998. Detailed global comparisons are made with path delays derived from the special sensor microwave imager (SSM/I) instruments and a network of 15 island radiosondes. The results provide consistent evidence that the TMR path delay measurements included an instrument-related downward drift of 1.0-1.5 mm/yr between October 1992 and December of 1996. The four-year drift correlates with an upward drift seen in the coldest TMR 18-GHz brightness temperature time series and is further supported by independent comparisons of TMR with ERS-1 and 2, GPS, and the Harvest Platform water vapor radiometer measurements. From January 1997 through June 1998, no significant relative path delay drift between TMR and SSM/I is seen in the comparison data, although anomalies do appear in early 1998. In terms of accuracy, both the SSM/I and radiosonde comparisons indicate no significant (>2%) scale error in the TMR path delay. An overall bias of <10 mm mag be present, but the comparisons are not consistent in this determination.
TL;DR: The Kipp & Zonen NR-Lite as discussed by the authors is a newly designed domeless net radiometer designed for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project, which was rigorously field tested for over eight months during 1998.
Abstract: The Kipp & Zonen NR-Lite is a newly designed domeless net radiometer. In preparation for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project, the NR-Lite was rigorously field tested for over eight months during 1998. Seven NR-Lites were compared to an Eppley four-component PSP/PIR net radiometer system, a Kipp & Zonen four-component CNR1, and a REBS Q*7.1. Measurement problems associated with calibration, precipitation, cosine response, and wind-induced error were examined. Results conclude that the NR-Lite is well-suited for experiments where remote, long-term measurements of net radiation are required.
TL;DR: In this article, along-track scanning radiometer (ATSR) with its dual-view feature is able to correct for absorption effects in the clear atmosphere more precisely than previous instruments; hence, it is especially important in this case for the retrieved surface temperatures not to be cloud contaminated.
Abstract: Infrared radiometric measurements of surface parameters are prone to error if clouds are present in the observation path. The along-track scanning radiometer (ATSR) with its novel dual-view feature is able to correct for absorption effects in the clear atmosphere more precisely than previous instruments; hence, it is especially important in this case for the retrieved surface temperatures not to be cloud contaminated. The algorithms used for identifying cloud in the routine processing of the ATSR data are described. These tests rely heavily on the previous experience gained by using data from the Advanced Very High Resolution Radiometer (AVHRR). Modifications to the original AVHRR tests, and the new tests developed, are given in detail.
TL;DR: Demonstration of a capability for sea surface salinity will enhance the potential of this large antenna concept for other applications such as soil moisture and, by including higher frequencies, high resolution measurements of ocean winds, precipitation, sea-surface temperature, and sea-ice.
Abstract: Microwave radiometry and scatterometry are established techniques for surface remote sensing applications. Some applications, such as measurement of sea surface salinity (SSS), sea surface temperature (SST), and soil moisture, require low frequency observations (/spl sim/6 GHZ and below) for good sensitivity, and sensors with large antennas to achieve adequate spatial resolution. Potentially, benefits can be obtained by observing simultaneously with passive and active channels, at similar frequencies, viewing angles, and spatial resolutions, making use of the complementary information contained in the emissivity and backscattering signatures of land and ocean targets. In this study, the authors investigate a concept for combined passive and active multichannel sensing with high spatial resolution, high measurement sensitivity, and wide swath for frequent global coverage. The system consists of a lightweight, relating, deployable mesh antenna with offset feeds. The system specifications are designed primarily for the measurement of sea surface salinity, since this application drives the precision and calibration requirements and, like soil moisture, is a science measurement for which no spaceborne capability currently exists. Demonstration of a capability for sea surface salinity will enhance the potential of this large antenna concept for other applications such as soil moisture and, by including higher frequencies, high resolution measurements of ocean winds, precipitation, sea-surface temperature, and sea-ice.
TL;DR: In this article, the authors describe a low-noise infrared radiometer for measurements of atmosphere and ground surface targets, or CLIMAT, which is a highly sensitive field instrument designed to measure brightness temperatures or radiances in the infrared.
Abstract: The new infrared radiometer (conveyable low-noise infrared radiometer for measurements of atmosphere and ground surface targets, or CLIMAT) is a highly sensitive field instrument designed to measure brightness temperatures or radiances in the infrared, from the ground level, or from an aircraft. It can be equipped with up to six channels in the 8–14-μm range. This instrument is characterized by its portability (total mass less than 5 kg), its self-sufficiency, and its automated operation. It can be operated either manually or automatically. The optical head of the instrument contains an objective lens and a condenser mounted according to the Kohler design, providing a uniform irradiation on the detector and a well-delimited field of view. The radiation is measured by a low-noise fast thermopile whose responsivity is slightly temperature dependent. The radiometric noise expressed as an equivalent brightness temperature is on the order of 50 mK for a 1-μm bandwidth at room temperature. The applicat...
TL;DR: In this article, the authors presented the processing stream for aerosol retrievals over oceans from the visible and infrared scanner [VIRS; a five-channel radiometer similar to the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR)] aboard the TRMM satellite, launched in November 1997.
Abstract: This paper outlines the processing stream for aerosol retrievals over oceans from the visible and infrared scanner [VIRS; a five-channel radiometer similar to the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution Radiometer (AVHRR)] aboard the Tropical Rainfall Measuring Mission (TRMM) satellite, launched in November 1997. Emphasis is on 1) the applying the previously developed AVHRR second-generation aerosol retrieval algorithm to VIRS data to derive an aerosol parameter, indicative of particle size; 2) removing the unwanted “thermal leak” signal in the 1.61-μm channel; 3) giving examples of the first aerosol retrievals from space at this wavelength; and 4) assessing the accuracy of the retrievals with theoretical error analyses and empirical self- and interconsistency checks. Aerosol optical depths τA1 and τA2 are retrieved from reflected solar radiances in VIRS channels 1 and 2 centered at wavelengths λ1 = 0.63 and λ2 = 1.61 μm, using two independent lookup tables...
TL;DR: In this paper, a combination of passive microwave and radar observations from the TRMM satellite is used to investigate the consistency between the two sensors, and the results from a case in the central Pacific suggest that a crude consistency may be achieved if a different drop size is used for the radiometer and the radar.
Abstract: A combination of passive microwave and radar observations from the Tropical Rainfall Measuring Mission (TRMM) satellite is used to investigate the consistency between the two sensors. Rather than relying on some absolute ‘‘truth’’ to verify retrievals, this paper focuses on one assumption—namely, the drop size distribution (DSD)—and how different DSDs lead to improved or reduced consistency. Results from a case in the central Pacific suggest that a crude consistency may be achieved if a different drop size is used for the radiometer and the radar. In this particular case, a Marshall‐Palmer or a gamma distribution with the shape parameters properly set leads to similar results. Although this study offers no independent validation of its conclusions, it does demonstrate that rainfall validation need not be confined to surface rainfall measurements, which are only loosely related to the volumetric observations made by most sensors. As mean size distributions of raindrops are measured in the TRMM field experiments by disdrometers, profilers, multiparameter radars, and direct aircraft observations, the technique presented in this paper can be applied on a storm-by-storm basis, and conclusions can be verified directly.
TL;DR: It is demonstrated that the model simulations lead to a reliable identification of the radiometric configurations most sensitive to ground variables, which aid the development of a soil moisture inversion algorithm that performs well even with soils covered by developed vegetation.
Abstract: The microwave brightness temperatures of a wheat field were measured in 1993, during the whole growth cycle by the six-frequency PORTOS radiometer, at two polarizations and several angles. In this paper, the emissivities measured at L-, C-, X-, and K-band are compared with those simulated by a discrete multiple scattering model based on the radiative transfer theory. The agreement between experimental and simulated data is generally good at all frequencies, although a unique set of input parameters has been used. It is demonstrated that the model simulations lead to a reliable identification of the radiometric configurations most sensitive to ground variables. Moreover, they aid the development of a soil moisture inversion algorithm that performs well even with soils covered by developed vegetation.
TL;DR: In this paper, a simple model is described to derive surface temperature and sensible heat flux from the advanced very high resolution radiometer (AVHRR) data collected over an extensive site of semiarid grassland in northwest Mexico during the summer of 1997 as part of the semi-arid land-surface-atmosphere (SALSA) program.
01 Dec 2000
TL;DR: The Portable Apparatus for Rapid Acquisition of Bidirectional Observation of the Land and Atmosphere III (PARABOLA III) is a sphere-scanning radiometer as mentioned in this paper.
Abstract: The Portable Apparatus for Rapid Acquisition of Bidirectional Observation of the Land and Atmosphere III (PARABOLA III) is a sphere‐scanning radiometer. The original PARABOLA was built to study the relationship between surface morphology and reflected radiation properties. Follow‐on work led to the design of an improved radiometer, the PARABOLA III. This in‐situ sensor will be used to validate surface reflectances at angles measured by the Multi‐angle Imaging SpectroRadiometer (MISR), a global imager flown on the Earth Observing System (EOS)‐Terra orbital spacecraft. Derived PARABOLA III data products include the surface bidirectional reflectance factor, and sky and surface radiances for the upward and downward viewing hemispheres. This paper describes the design, calibration, and operation of the JPL PARABOLA III.
TL;DR: In this paper, a method of measuring the absolute spectral irradiance of quartz-halogen-tungsten lamps is described, based on the known responsivity of a filter radiometer, the components of which are separately characterized.
Abstract: A method of measuring the absolute spectral irradiance of quartz-halogen-tungsten lamps is described, based on the known responsivity of a filter radiometer, the components of which are separately characterized. The characterization is described for the wide wavelength range essential for deriving the spectrum of a lamp, from 260 nm to 950 nm. Novel methods of interpolation and measurement are implemented for the spectral responsivity of the filter radiometer. The combined standard uncertainty of spectral irradiance measurements is less than 1.4 parts in 102 from 290 nm to 320 nm (ultraviolet B) and 4 parts in 103 from 440 nm to 900 nm (visible to near-infrared). As an example, the derived spectral irradiances of two lamps measured at the Helsinki University of Technology (HUT, Finland) are presented and compared with the measurement results of the National Institute of Standards and Technology (NIST, USA) and the Physikalisch-Technische Bundesanstalt (PTB, Germany). The comparisons indicate that the HUT spectral irradiance scale is between those of the NIST and the PTB in the wavelength range 290 nm to 900 nm. The long-term reproducibility of the spectral irradiance measurements is also presented. Over a period of two years, the reproducibility appears to be better than 1 part in 102.
TL;DR: In this article, the authors proposed a method of simultaneously retrieving ice water path and mass median diameter using microwave data at two frequencies for tropical non-precipitating clouds, which effectively allows ice particle density to decrease with particle size.
Abstract: The method of simultaneously retrieving ice water path and mass median diameter using microwave data at two frequencies is examined and implemented for tropical nonprecipitating clouds. To develop the retrieval algorithm, the authors first derived a bulk mass–size relation for ice particles in tropical clouds based on microphysical data collected during the Central Equatorial Pacific Experiment. This relation effectively allows ice particle density to decrease with particle size. In implementing the retrieval algorithm, 150- and 220-GHz Millimeter-Wave Imaging Radiometer data collected during the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment were used. Ice water path and mass median diameter are determined based on a lookup table generated by a radiative transfer model. The lookup table depends on cloud type, cloud liquid water path, and atmospheric temperature and humidity profiles. Only nonprecipitating clouds are studied in this paper. Error analyses were pe...
01 Oct 2000
TL;DR: The SeaWiFS Transfer Radiometer (SXR) as mentioned in this paper is a multichannel radiometer designed to verify and compare measurements of spectral radiance at six discrete wavelengths in the visible and near infrared for various calibration sources.
Abstract: The SeaWiFS Transfer Radiometer (SXR) was built for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project as part of an Interagency Agreement with the National Aeronautics and Space Administration (NASA). The SXR is a multichannel radiometer designed to verify and compare measurements of spectral radiance at six discrete wavelengths in the visible and near infrared for various calibration sources in the SeaWiFS Project. In addition, the SXR is used to compare these sources to standards of spectral radiance maintained at the National Institute of Standards and Technology (NIST). The SXR was designed, built, and thoroughly characterized in the Optical Technology Division at NIST. A unique optical design provides six independent optical paths, each equipped with a temperature stabilized interference filter and silicon photodiode. A separate beam path through the input lens is used to visually align the SXR. The entrance windows for each channel overlap at the source, with each channel sampling a unique solid angle within the field of view of the SXR; this allows for simultaneous sampling of all channels. The combined standard relative uncertainty of spectral radiance measurements with the SXR is estimated to be between 0.6% and 1.3%. This report describes the design and construction of the SXR in detail, and gives the results of the optical characterization and calibrations done at NIST. The SXR has been used for several intercomparisons which include several SeaWiFS Intercalibration Round-Robin Experiments (SIRREXs); those done at the Marine Optical Buoy (MOBY) laboratories in Honolulu, Hawaii; at the NEC Corporation in Yokohama, Japan; and Orbital Sciences Corporation (OSC) in Germantown, Maryland. Thorough optical characterization and calibration of the SXR was essential to the successful application of the radiometer for these measurements.
TL;DR: The microwave radiometer serves as a promising instrument for monitoring temperatures at depth away from the catheter-electrode tip in ablative therapy for cardiac arrhythmias and can estimate distant temperatures by detecting microwave electromagnetic radiation.
Abstract: Introduction: Current techniques for estimating catheter tip temperature in ablative therapy for cardiac arrhythmias rely on thermocouples or thermistors attached to or embedded in the tip electrode These methods may reflect the electrode temperature rather than the tissue temperature during electrode cooling so that the highest temperature away from the ablation site may go undetected A microwave radiometer is capable of detecting microwave radiation as a result of molecular motion In this study, we evaluated microwave radiometric thermometry as a new technique to monitor temperature away from the electrode tip during ablative therapy utilizing a saline model Methods and Results: A microwave radiometer antenna and fluoroptic thermometer were inserted in a test tube with circulating room temperature saline kept constant at 235°C while the surrounding saline bath was heated from 37°C to 70°C For every degree rise in the warm saline bath placed either 5mm or 8mm from the radiometer antenna, the radiometer temperature changed 026°C and 014°C respectively while the fluoroptic temperature probe remained constant at 235°C The radiometer temperature was highly correlated with the warm saline bath temperature (R2=0997 for warm saline 5mm from the antenna, R2=0991 for warm saline 8mm from the antenna) Conclusions: Microwave radiometry can estimate distant temperatures by detecting microwave electromagnetic radiation The sensitivity of the microwave radiometer is also distance-dependent The microwave radiometer thus serves as a promising instrument for monitoring temperatures at depth away from the catheter-electrode tip in ablative therapy for cardiac arrhythmias
TL;DR: In this paper, the upwelling radiation in an open-canopied juniper-sagebrush ecosystem was measured with the eddy covariance technique. But, the authors pointed out that the vegetation structure around the measurement location can be highly variable.
11 Jun 2000
TL;DR: In this article, the design, performance and manufacturing of 140 InP HFET amplifiers suitable for cryogenic cooling are described, which exhibit low noise performance and complex gain match over the given radiometer bandwidths (typical noise temperature of 90 K or 1.2 dB noise figure, for W-band amplifier at 80 K ambient).
Abstract: Differential pseudo-correlation radiometers covering 20-25 GHz, 28-37 GHz, 35-46 GHz, 53-69 GHz and 82-106 GHz are used in the Microwave Anisotropy Probe (MAP) mission to be launched in late 2000. This paper describes the design, performance and manufacturing of 140 InP HFET amplifiers suitable for cryogenic cooling which exhibit low noise performance and complex gain match over the given radiometer bandwidths (typical noise temperature of 90 K, or 1.2 dB noise figure, for W-band amplifier at 80 K ambient).
TL;DR: In this paper, the authors minimized systematic errors in the time series introduced by satellite orbital drift in an objective manner with the help of the onboard warm-blackbody temperature, which is used in the calibration of the MSU radiometer.
Abstract: Observations made in Channel 2 (53.74 GHz) of the Microwave Sounding Unit (MSU) radiometer, flown onboard sequential, sun-synchronous, polar-orbiting NOAA (National Oceanic and Atmospheric Administration) operational satellites, indicate that the mean temperature of the atmosphere over the globe increased during the period 1980 to 1999. In this study, we have minimized systematic errors in the time series introduced by satellite orbital drift in an objective manner. This is done with the help of the onboard warm-blackbody temperature, which is used in the calibration of the MSU radiometer. The corrected MSU Channel 2 observations of the NOAA satellite series reveal that the vertically-weighted global-mean temperature of the atmosphere, with a peak weight near the mid troposphere, warmed at the rate of 0.13 +/- 0.05 K/decade during 1980 to 1999. The global warming deduced from conventional meteorological data that have been corrected for urbanization effects agrees reasonably with this satellite-deduced result.