Showing papers on "Radiometer published in 1999"

Retrieval of land surface parameters using passive microwave measurements at 6-18 GHz

Abstract: An approach is evaluated for retrieval of land surface parameters (soil moisture, vegetation water content, and surface temperature) using satellite microwave radiometer data in the 6-18 GHz frequency range. The approach is applicable to data that will be acquired by the Advanced Microwave Scanning Radiometer (AMSR), planned for launch on the Japanese Advanced Earth Observing Satellite (ADEOS)-II and Earth Observing System (EOS) PM-1 platforms in 1999 and 2000, respectively. The retrieval method is based on a radiative transfer (RT) model for land-surface and atmospheric emission, with model coefficients that can be tuned over specific calibration regions and applied globally. The method uses an iterative, least-squares algorithm, based on six channels of radiometric data. Simulations using this algorithm indicate that, for an assumed sensor noise of 0.3 K in all channels, soil moisture and vegetation water content retrieval accuracies of 0.06 g cm/sup -3/ and 0.15 kg m/sup -2/, respectively, should be achievable in regions of vegetation water content less than approximately 1.5 kg m/sup -2/. A surface temperature accuracy of 2 C should be achievable, except for bare soils, where discrimination between moisture and temperature variability is difficult using this algorithm. These accuracies are for retrievals averaged over the sensor footprint, and they exclude conditions of precipitation, open water, snow cover, frozen ground, or high topographic relief within the footprint. The algorithm has been tested using data from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) for the years 1982-1985, over the African Sahel, and the retrieval results compared to output from an operational numerical weather prediction model.

Results of POLDER in-flight calibration

Abstract: POLDER is a CNES instrument on board NASDA's ADEOS polar orbiting satellite, which was successfully launched in August 1996. On October 30, 1996, POLDER entered its nominal acquisition phase and worked perfectly until ADEOS's early end of service on June 30, 1997. POLDER is a multispectral imaging radiometer/polarimeter designed to collect global and repetitive observations of the solar radiation reflected by the Earth/atmosphere system, with a wide field of view (2400 km) and a moderate geometric resolution (6 km). The instrument concept is based on telecentric optics, on a rotating wheel carrying 15 spectral filters and polarizers, and on a bidimensional charge coupled device (CCD) detector array. In addition to the classical measurement and mapping characteristics of a narrow-band imaging radiometer, POLDER has a unique ability to measure polarized reflectances using three polarizers (for three of its eight spectral bands, 443 to 910 nm) and to observe target reflectances from 13 different viewing directions during a single satellite pass. One of POLDER's original features is that its in-flight radiometric calibration does not rely on any on-board device. Many calibration methods using well-characterized calibration targets have been developed to achieve a very high calibration accuracy. This paper presents the various methods implemented in the in-flight calibration plan and the results obtained during the instrument calibration phase: absolute calibration over molecular scattering, interband calibration over sunglint and clouds, multiangular calibration over deserts and clouds, intercalibration with Ocean Color and Temperature Scanner (OCTS), and water vapor channels calibration over sunglint using meteorological analysis. A brief description of the algorithm and of the performances of each method is given.

Angular variation of thermal infrared emissivity for some natural surfaces from experimental measurements

Abstract: Multiangle algorithms for estimating sea and land surface temperature with Along-Track Scanning Radiometer data require a precise knowledge of the angular variation of surface emissivity in the thermal infrared. Currently, few measurements of this variation exist. Here an experimental investigation of the angular variation of the infrared emissivity in the thermal infrared (8-14-microm) band of some representative samples was made at angles of 0 degrees-65 degrees (at 5 degrees increments) to the surface normal. The results show a decrease of the emissivity with increasing viewing angle, with water showing the highest angular dependence (approximately 7% from 0 degrees to 65 degrees views). Clay, sand, slime, and gravel show variations of approximately 1-3% for the same range of views, whereas a homogeneous grass cover does not show angular dependence. Finally, we include an evaluation of the impact that these data can produce on the algorithms for determining land and sea surface temperature from double-angle views.

Atmospheric Latent Heating Distributions in the Tropics Derived from Satellite Passive Microwave Radiometer Measurements

Abstract: A method for the remote sensing of three-dimensional latent heating distributions in precipitating tropical weather systems from satellite passive microwave observations is presented. In this method, cloud model simulated hydrometeor/latent heating vertical profiles that have radiative characteristics consistent with a given set of multispectral microwave radiometric observations are composited to create a best estimate of the observed profile. An estimate of the areal coverage of convective precipitation within the radiometer footprint is used as an additional constraint on the contributing model profiles. This constraint leads to more definitive retrieved profiles of precipitation and latent heating in synthetic data tests. The remote sensing method is applied to Special Sensor Microwave/Imager (SSM/I) observations of tropical systems that occurred during the TOGA COARE Intensive Observing Period, and to observations of Hurricane Andrew (1992). Although instantaneous estimates of rain rates are high-biased with respect to coincident radar rain estimates, precipitation patterns are reasonably correlated with radar patterns, and composite rain rate and latent heating profiles show respectable agreement with estimates from forecast models and heat and moisture budget calculations. Uncertainties in the remote sensing estimates of precipitation/latent heating may be partly attributed to the relatively low spatial resolution of the SSM/I and a lack of microwave sensitivity to tenuous anvil cloud, for which upper-tropospheric latent heating rates may be significant. Estimated latent heating distributions in Hurricane Andrew exhibit an upper-level heating maximum that strengthens as the storm undergoes a period of intensification.

Radiative transfer modeling for the EOS Terra satellite Measurement of Pollution in the Troposphere (MOPITT) instrument

Abstract: This paper describes the radiative transfer modeling effort in support of the EOS Measurements of Pollution in the Troposphere (MOPITT) instrument. MOPITT is due to be launched on the AM-1 Terra platform in the summer of 1999 and is a nadir-viewing gas correlation radiometer designed to measure CO and CH4 in the troposphere using a CO thermal channel at 4.7 μm and reflected solar channels for CO at 2.3 μm and CH4 at 2.2 μm. We describe the spectroscopic considerations and radiative transfer studies that have been performed for this instrument and the implications for operational algorithm design. We outline the construction of MOPITT project forward models, both the research codes and the fast transmittance module that forms part of the operational retrieval algorithm. Several different approaches have been considered for these models: full line-by-line calculations using the general purpose line-by-line transmittance and radiance model GENLN2, absorption coefficient look-up tables, and regression techniques using a recurrence parameterization of transmittance. These models are capable of reproducing MOPITT channel signals and their dependence on temperature, viewing geometry, and the mixing ratios of target and contaminating gases.

Satellite remote sensing of soil moisture in Illinois, United States

Abstract: To examine the utility of using satellite passive microwave observations to measure soil moisture over large regions, we conducted a pilot study using the scanning multichannel microwave radiometer (SMMR) on Nimbus-7, which operated from 1978 to 1987, and actual in situ soil moisture observations from the state of Illinois, United States, which began in 1981. We examined SMMR midnight microwave brightness temperatures on a 0.5° × 0.5° grid, and compared them with direct soil moisture measurements at 14 sites in Illinois for the period 1982–1987. The results suggest that both the polarization difference and the microwave emissivity for horizontal polarization at frequencies ≤18 GHz have real utility for use as a soil moisture information source in regions with grass or crops where the vegetation is not too dense. While SMMR observations ended in 1987, special sensor microwave/imager observations at 19 GHz start then and extend to the present, and advanced microwave scanning radiometer instruments will fly on satellites beginning soon. Together with SMMR, they have the potential to produce a soil moisture record over large regions for more than two decades and extend it into the future. Satellite observations from these low-resolution satellite instruments measure the component of large-scale long-term soil moisture variability that is related to atmospheric forcing (from precipitation, evapotranspiration, and snowmelt).

Toward the elimination of bias in satellite retrievals of sea surface temperature: 1. Theory, modeling and interalgorithm comparison

Abstract: The along-track scanning radiometer (ATSR), launched in July 1991 on ERS-1, is an infrared radiometer designed to permit retrieval of skin sea surface temperature (SST) to the accuracy required for many climate research purposes. Using the prelaunch retrieval scheme, this accuracy (0.3 K) was achieved only when observations at 3.7 μm were available, i.e., SSTs derived from nighttime scenes before the failure of this channel in May 1992. Retrievals using only channels at 11 and 12 μm suffered significant biases. First, cold biases of up to 1.5 K arose from the radiative effects of the unanticipated presence of a significant loading of stratospheric aerosol following the eruption of Mount Pinatubo in June 1991. Second, cold biases of up to 0.4 K were associated with regions of high water vapor loading. We solve the first problem by choosing retrieval coefficients to be orthogonal to the modeled changes in brightness temperatures caused by variations in stratospheric aerosol optical depth. We attribute the second problem to deficiencies in radiative transfer modeling of water vapor continuum absorption and show that use of an updated parameterization reduces bias from wet atmospheres. Applying the new retrieval coefficients to ATSR data, we find good consistency between SSTs retrieved with and without the 3.7 μm channels, the global mean and standard deviation of differences between retrievals being of the order of 0.05 K and 0.25 K, respectively. We therefore anticipate that reprocessing ATSR data using our new retrieval scheme will result in a substantially improved record of ATSR SST, in that the following should be reduced to insignificant levels: (1) the artefactual trend (previously -0.25 K yr -1 in tropical regions) corresponding to the decaying load of post-Pinatubo aerosol, (2) the discontinuity in SST retrievals (previously up to 0.7 K) associated with the failure of the 3.7 μm channel, and (3) cold biases (previously ∼0.4 K) in wet tropical regions. Thus this work represents a significant advance in terms of the quality of ATSR SSTs for climate research. The techniques are also applicable to both the ATSR-2, flying on ERS-2, and the advanced ATSR (planned for launch on the Envisat platform in 2000). However, we note that even with the improved physical modeling on which the new retrieval coefficients are based, we do not yet meet the stringent requirement of 0. K decade -1 stability in retrievals for climate change detection purposes.

Deriving meteorological variables across Africa for the study and control of vector-borne disease: a comparison of remote sensing and spatial interpolation of climate

Abstract: This paper presents the results of an investigation into the utility of remote sensing (RS) using meteorological satellites sensors and spatial interpolation (SI) of data from meteorological stations, for the prediction of spatial variation in monthly climate across continental Africa in 1990. Information from the Advanced Very High Resolution Radiometer (AVHRR) of the National Oceanic and Atmospheric Administration's (NOAA) polar-orbiting meteorological satellites was used to estimate land surface temperature (LST) and atmospheric moisture. Cold cloud duration (CCD) data derived from the High Resolution Radiometer (HRR) on-board the European Meteorological Satellite programme's (EUMETSAT) Meteosat satellite series were also used as a RS proxy measurement of rainfall. Temperature, atmospheric moisture and rainfall surfaces were independently derived from SI of measurements from the World Meteorological Organization (WMO) member stations of Africa. These meteorological station data were then used to test the accuracy of each methodology, so that the appropriateness of the two techniques for epidemiological research could be compared. SI was a more accurate predictor of temperature, whereas RS provided a better surrogate for rainfall; both were equally accurate at predicting atmospheric moisture. The implications of these results for mapping short and long-term climate change and hence their potential for the study and control of disease vectors are considered. Taking into account logistic and analytical problems, there were no clear conclusions regarding the optimality of either technique, but there was considerable potential for synergy.

Synthetic aperture radiometer systems

Abstract: Aperture synthesis is an emerging technology for passive microwave remote sensing from space. It is an interferometric technique similar to earth rotation synthesis employed in radio astronomy in which pairs of small antennas and signal processing are used to obtain the resolution of a single large antenna. The technique has the potential to overcome the barriers that antenna size has plated on passive microwave remote sensing from space. The technique has been demonstrated successfully for remote sensing at L-band with the aircraft prototype ESTAR. New aircraft instruments are under development and proposals have been submitted for instruments to demonstrate this technology in space.

Aerosol optical depth retrieval using ATSR-2 and AVHRR data during TARFOX

Abstract: Satellite retrieved aerosol optical properties are compared to aircraft measurements for a case study during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) Two satellite instruments are used: the Along Track Scanning Radiometer 2 (ATSR-2) and the advanced very high resolution radiometer (AVHRR) The aerosol optical depth in the mid-visible (0555 μm) retrieved from the ATSR-2 data agrees within 003 with colocated sunphotometer measurements Also, the spectral behavior of the aerosol optical depth is retrieved accurately Good correlation is found between aerosol optical depths for AVHRR channel 1 (064 μm) and sunphotometer derived values, but the satellite retrieved values are 005 to 015 lower The Angstrom wavelength exponent is determined both from the ATSR-2 and the AVHRR data The ATSR-2 derived Angstrom exponents are in good agreement with the values computed from the sunphotometer data The Angstrom exponents determined from AVHRR data show very large variations Both the ATSR-2 and the AVHRR aerosol optical depth images show a large gradient Vertical profile data of temperature, relative humidity, and particle scattering indicate that this gradient is probably caused by changes in the dry aerosol properties, rather than a change in the relative humidity Copyright 1999 by the American Geophysical Union

Ice and snow-type classification in the Vestfold Hills, East Antarctica, using Landsat-TM data and ground radiometer measurements

Abstract: The aim of the present project was to find simple satellite-based methods to be used in glaciological-climatological research in Antarctica. A Landsat-TM image from 16 February 1991 was used together with field data to study the spectral charcateristics of different types of snow and ice in the Vestfold Hills, East Antarctica (68degrees35'S, 78degrees10'E). Radiometer measurements were made simultaneously with the satellite passage and at several other occasions using a handheld Photodyne 44XLA. 72 test sites selected in the Landsat-TM image formed the basis for the analysis of the spectral characteristics. Principal component analysis, ratioing, and maximum-likelihood classification were also performed. The analysis revealed a large and interesting information content in the TM image. Blue-ice of different character as well as snow of various degree of metamorphosis were discernible and could also be mapped using maximumlikelihood classification. The TM-3/TM-4-ratio was found to be a simple tool for dist...

Effect of curing-tip diameter on the accuracy of dental radiometers.

Abstract: The purpose of this study was to determine the accuracy of four commercially available radiometers when curing tips of different diameters were used. A visible-light curing unit (Optilux 500) with a new 80-watt quartz-halogen bulb (OptiBulb) was used as the light source for all measurements. The unit's irradiance value was measured using three hand-held radiometers (Demetron model #100, Cure-Rite model #644726, and Coltolux Light Meter) and a built-in visible-light curing unit radiometer (Optilux 500). Measurements were made with four curing tips of diameters 4 mm, 7.5 mm, 10.5 mm, and 12 mm. For each tip, trials were made with five radiometers of each model. Student's t-tests at the 0.05 level of significance were used to compare the mean irradiance measured by each model of radiometer, to the irradiance value measured by a laboratory-grade power meter. A one-way analysis of variance at the 0.05 level of significance was used to compare the irradiance values among the five samples of each commercially available radiometer model. Except for the Optilux 500 built-in radiometer with the 10.5-mm tip, all the commercially available radiometers exhibited irradiance values significantly different from those of the laboratory-grade power meter. There were no statistically significant differences among the five samples of each commercially available radiometer model.

A New Look at Calibration and Use of Eppley Precision Infrared Radiometers. Part II: Calibration and Use of the Woods Hole Oceanographic Institution Improved Meteorology Precision Infrared Radiometer*

Abstract: For some years, investigators have made measurements of downwelling longwave irradiance with the Eppley Precision Infrared Radiometer (PIR), recording the values of thermopile voltage and body and dome thermistor resistances and combining them in data processing. Part I of this paper reviews previous work on the processing equation and presents an improved equation. It establishes that the standard single-output Eppley has an inherent uncertainty of 5%. By measuring the three possible outputs separately and comparing them in the improved equation, the inherent accuracy can be improved to 1.5%. Part II presents a method of calibrating the Eppley PIR for the three-output equation using an easily constructed blackbody cavity in a temperature bath capable of a 0°–50°C temperature range. Calibration of PIR thermistors is recommended since occasionally one is found out of specifications. An outdoor comparison of 15 PIRs calibrated with the technique was carried out in groups of four, with one PIR used ...

Sensitivity of a 1.4 GHz direct-sampling digital radiometer

Abstract: This paper presents a novel direct RF sampling receiver architecture that will greatly facilitate the implementation of higher spatial resolution satellite radiometers for improved near-term climate forecasting. Direct-sampling is especially suitable for integration onto the distributed, multiple element platform used in L-band synthetic thinned array radiometry (STAR). To evaluate the direct-sampling concept, the authors have developed a statistical model that predicts the worst case radiometric sensitivity for a 1.4 GHz digital receiver. Theoretical results show that only 2-3 bits of converter resolution are needed to approach the performance of an ideal analog radiometer and that sampling jitter will not significantly degrade the performance of STAR.

Comparison of column ozone retrievals by use of an UV multifilter rotating shadow-band radiometer with those from Brewer and Dobson spectrophotometers.

Abstract: The U.S. Department of Agriculture UV-B Monitoring Program measures ultraviolet light at seven wavelengths from 300 to 368 nm with an ultraviolet multifilter rotating shadow-band radiometer (UV-MFRSR) at 25 sites across the United States, including Mauna Loa, Hawaii. Column ozone has been retrieved under all-sky conditions near Boulder, Colorado (40.177 °N, 105.276 °W), from global irradiances of the UV-MFRSR 332- and 305-nm channels (2 nm FWHM) using lookup tables generated from a multiple-scattering radiative transfer code suitable for solar zenith angles (SZA’s) up to 90°. The most significant sources of error for UV-MFRSR column ozone retrievals at SZA’s less than 75° are the spectral characterizations of the filters and the absolute calibration uncertainty, which together yield an estimated uncertainty in ozone retrievals of ±4.0%. Using model sensitivity studies, we determined that the retrieved column ozone is relatively insensitive (<±2%) to typical variations in aerosol optical depth, cloud cover, surface pressure, stratospheric temperature, and surface albedo. For 5 months in 1996–1997 the mean ratio of column ozone retrieved by the UV-MFRSR divided by that retrieved by the collocated Brewer was 1.024 and for the UV-MFRSR divided by those from a nearby Dobson was 1.025. The accuracy of the retrieval becomes unreliable at large SZA’s of more than 75° as the detection limit of the 305-nm channel is reached and because of overall angular response errors. The UV-MFRSR advantages of relatively low cost, unattended operation, automated calibration stability checks using Langley plots, and minimal maintenance make it a unique instrument for column ozone measurement.

Ultraviolet Radiometry With Synchrotron Radiation and Cryogenic Radiometer

Abstract: The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.

The Calibration and Intercalibration of Sea-Going Infrared Radiometer Systems Using a Low Cost Blackbody Cavity

Abstract: There are many infrared radiometer systems available for the measurement of in situ sea surface skin temperature (SSST). Unfortunately, the marine environment is extremely hostile to optical components, and to ensure the accuracy of SSST measurements, an absolute calibration of instrumentation using an independent calibration reference is required both before and after any sea deployment. During extended deployments it is prudent to have additional regular calibration data to monitor instrument performance characteristics. This paper presents a design for an ambient temperature (278–325 K), wide aperture (100 mm), reference blackbody unit that may be used to calibrate a variety of sea-going infrared radiometer systems both in the laboratory and in the field. The blackbody consists of a spun copper cavity coated with well-characterized high emissivity paint (Mankiewicz Nextel Velvet Coating 811-21) immersed in a water bath that is continuously mixed using a strong water pump. The radiant temperatu...

Ultraviolet radiometry with synchrotron radiation and cryogenic radiometry

Abstract: The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.

Thermal-infrared field radiometer for vicarious cross-calibration : characterization and comparisons with other field instruments

Abstract: A four-band (8.2 to 9.2, 10.5 to 11.5, 11.5 to 12.5, and 8 to 14 mm), prototype, thermal-IR radiometer, model CE 312 (CE 312 is the company model number. In previous papers, the CE 312 was called the CLIMAT (conveyable low-noise IR radiometer for measurements of at- mosphere and ground-surface targets)), with a built-in radiance refer- ence is been fabricated by CIMEL Electronique (Paris, France) for use as a field instrument. The instrument is briefly described, laboratory char- acterization is detailed, and its field measurements are compared with those from three other radiometers. The CE 312's main characteristics are linearity of better than 0.8%, field of view of 9.5 deg; noise-equivalent temperature difference of 0.06 to 0.2 K (depending on the band) for brightness temperatures of 0 to 75°C; SNR greater than 1100 for the broadband and greater than 400 for the other bands for brightness tem- peratures between 10 and 80°C; and repeatability of the measured radi- ance smaller than 0.35% after four field campaigns, corresponding to 0.2 K in terms of brightness temperature. Field measurements were con- ducted over different periods during 1996 at Jornada Experimental Range, New Mexico, Lunar Lake and Railroad Valley, Nevada, and Lake Tahoe, California. The CE 312 compares quite favorably with the other instruments: the brightness temperature at two different sites compared to within 0.3 K with two instruments. These measurements show that the CE 312 thermal-IR radiometer is very stable for ambient temperatures varying between 15 and 60°C and that the availability of several filters in the thermal-IR region can help tremendously to improve the accuracy of the radiance determination. © 1999 Society of Photo-Optical Instrumentation Engi- neers. (S0091-3286(99)01902-9)

Electron cyclotron emission diagnostics on the large helical device

Abstract: The electron cyclotron emission (ECE) diagnostic system is installed on the large helical device (LHD). The system includes the following instruments: a heterodyne radiometer, a Michelson spectrometer, and a grating polychromator. A 63.5 mm corrugated waveguide system is fully utilized. Large collection optics and notch filters at the frequency of the LHD electron cyclotron heating (ECH) were developed for this system. In addition to these filters, the rectangular waveguide notch filters, the ECE measurement with the radiometer has been successfully performed during the ECH.

Analyses of Atmospheric Radiation Measurement (ARM) program's Enhanced Shortwave Experiment (ARESE) multiple data sets for studying cloud absorption

Abstract: Following the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE), some studies reported a cloud absorption anomaly (CAA) of unprecedented magnitude. The largest discrepancy was found on a heavy overcast day (October 30, 1995) when cloud absorptance inferred from aircraft observations was 37% of the incoming solar irradiance, almost twice that of model calculations. The essential measurements supporting the finding were made with an airborne total solar broadband radiometer (TSBR). A thorough analysis is performed here, employing a variety of observations from more sources including aircraft, spacecraft, and ground-based instruments. It is found that albedos measured with the TSBR are systematically less than those inferred from other instruments. The difference in mean albedo between TSBR and that inferred from the scanning spectral polarimeter (SSP) on board the same aircraft amounts to 0.15, which is comparable to the reported CAA. SSP data were validated by (1) comparing them to data from the total direct diffuse radiometer (TDDR) spectral radiometer, (2) comparing the SSP's albedo-transmittance slope with that derived from ScaRaB satellite data, and (3) comparing SSP-derived albedos with those inferred from cloud optical parameters estimated from ground-based passive and active observations. All these comparisons show that SSP data are consistent with other measurements within the data uncertainties whose accumulated upper limit is <0.06. A reasonable doubt is thus cast on the claim of a very strong cloud absorption anomaly found using TSBR data on October 30.

Calibration and data elaboration procedure for sky irradiance measurements.

Abstract: The problems encountered in the elaboration of measurements of direct and sky diffuse solar irradiance are the following: (1) to carry out the calibration for the direct irradiance, which consists in determining the direct irradiance at the upper limit of the atmosphere; (2) to carry out the calibration for the diffuse irradiance, which consists in determining the solid viewing angle of the sky radiometer; (3) to determine the input parameters, namely, ground albedo, real and imaginary parts of the aerosol refractive index, and aerosol radius range; and (4) to determine from the optical data the columnar aerosol optical depth and volume radius distribution. With experimental data and numerical simulations a procedure is shown that enables one to carry out the two calibrations needed for the sky radiometer, to determine a best estimate of the input parameters, and, finally, to obtain the average features of the atmospheric aerosols. An interesting finding is that inversion of only data of diffuse irradiance yields the same accuracy of result as data of both diffuse and direct irradiance; in this case, only calibration of the solid viewing angle of the sky radiometer is needed, thus shortening the elaboration procedure. Measurements were carried out in the Western Mediterranean Sea (Italy), in Tokyo (Japan), and in Ushuaia (Tierra del Fuego, Argentina); data were elaborated with a new software package, the Skyrad code, based on an efficient radiative transfer scheme.

Advanced Spaceborne Thermal Emission & Reflection Radiometer Algorithm Theoretical Basic Document for: An Atmospheric Correction Method for ASTER Thermal Radiometry Over Land

Abstract: The objectives of the ASTER investigation in the thermal infrared include, among other things, providing estimates of the radiance leaving the land surface.

Domain-engineered pyroelectric radiometer

Abstract: We built a large-area domain-engineered pyroelectric radiometer with high spatial and spectral response uniformity that is an excellent primary transfer standard for measurements in the near- and the mid-infrared wavelength regions. The domain engineering consisted of inverting the spontaneous polarization over a 10-mm-diameter area in the center of a uniformly poled, 15.5 mm x 15.5 mm square, 0.25-mm-thick LiNbO(3) plate. Gold black was used as the optical absorber on the detector surface, and an aperture was added to define the optically sensitive detector area. Our results indicate that we significantly reduced the acoustic sensitivity without loss of optical sensitivity. The detector noise equivalent power was not exceptionally low but was nearly constant for different acoustic backgrounds. In addition, the detector's spatial-response uniformity variation was less than 0.1% across the 7.5-mm-diameter aperture, and reflectance measurements indicated that the gold-black coating was spectrally uniform within 2%, from 800 to 1800 nm. Other detailed evaluations of the detector include detector responsivity as a function of temperature, electrical frequency response, angular response, and field of view.

Remote sensing of cirrus radiative parameters during EUCREX'94. Case study of 17 April 1994. Part I : Observations

Abstract: During the intensive European Cloud and Radiation Experiment 1994 (EUCREX’94) conducted off the coast of Brittany (France) over the Atlantic Ocean during April 1994, natural cirrus have been analyzed from in situ and remote sensing measurements. The authors have particularly studied the case of 17 April 1994. For this day a cirrus bank is described by a complete dataset, that is, classic airborne thermodynamical measurements, microphysical (forward scattering spectrometer probe) and OAP-2D2-C (optical array probe-cloud) probes manufactured by Particle Measuring System, and radiative (Barnes Precision Radiation Thermometer, Eppley pyranometers, and upward- and downward-looking pyrgeometers) measurements above and below the cloud. More specific airborne instruments were used such as upward backscatter lidar with polarization capabilities (LEANDRE) on board the Avion de Recherches Atmospheriques et Teledetection and the Polarization and Directionality of the Earth’s Reflectances (POLDER) radiometer ...

Simultaneous Land Surface Temperature–Emissivity Retrieval in the Infrared Split Window

Abstract: A combined land surface temperature–emissivity retrieval algorithm is developed and tested for Geostationary Operational Environmental Satellite (GOES)-Imager and National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (AVHRR) split-window channels. By assuming that the spectral emissivities are constant over a short time period (12–24 h), two sets of split-window radiance measurements taken at two different times are used to retrieve two spectral emissivities and two land surface temperatures (LSTs) simultaneously. The algorithm employs an optimization scheme rather than a direct solver for a system of equations because of constraint requirements. The retrieved variables minimize the rms differences between measured satellite radiances and those predicted by a spectrally detailed radiative transfer model. A GOES-8 version of the algorithm is validated with in situ radiometer measurements from the Department of Energy’s Atmospheric Radiation Measurement Program Cl...

Entropic Approach to Edge Detection for SST Images

Abstract: A new method designed for the detection of mesoscale structures in sea surface temperature (SST) satellite images, to be used in different applications such as climatic and environmental studies or fisheries, is presented. The method is based on an entropic approach technique to edge detection, using the Jensen–Shannon divergence. It is found to be an excellent edge detector technique that exhibits favorable characteristics. For example, it is very robust against impulsive and Gaussian noise, avoiding the use of previous filtering, with the subsequent gain in computational work and edge sharpness. The method is evaluated on a set of Advanced Very High-Resolution radiometer images of the Atlantic Ocean and Mediterranean Sea, near the Iberian Peninsula area. The SST fields have been generated using a split-window technique to avoid the problem of atmospheric disturbance; emissivity correction has been carried out to improve the reliability of the data. The results have been compared to those obtain...

Surface Based Radiometer (SBR) Data Acquisition System

Abstract: Since 1981, the Canadian Ice Service (CIS) has been conducting research into the use of microwave radiometers for the detection and monitoring of sea ice. The CIS has developed a Surface Based Radiometer (SBR) System which includes three dual polarized microwave radiometers (at 19, 37 and 85GHz). This remote sensing platform is truly mobile and has been deployed both on the ground and onboard icebreakers. It can be accessed and fully controlled remotely over a telephone line, through the Internet (TCP/IP) or via a wireless LAN connection using a data radio link. The focus of this paper is on the engineering, design and operationof the SBR system including some of the current applications of the system. In particular, the remote access, control, and near real-time data processing functions will be described.

The ROCSAT-1 IPEI Preliminary Results: Vertical Ion Drift Statistics

Abstract: A number of ground-based instruments,including 19.5GHz radiometer,optical raingauge,portable weather station,and high resolutiondisdrometer,were set up to conduct the Ka band propagation experimentof the Experimental Communication Payload(ECP)for ROCSAT-1.Inthis article,19.5GHz background sky noise temperatures measured atChung-Li and Tainan sites are presented and investigated.Long-term statisticsof the 19.5GHz background sky noise temperature observed by avertically pointed radiometer in precipitation-free condition over the Taiwanarea shows that the percentages of time that the sky noise temperatureexceeds 20K,30K,40K and 50K are,respectively,98%,85%,53%,and27%.However,in precipitating environments,statistics shows that the percentageof time that the sky noise temperature exceeds 55K,100K,150K,and 200K are,respectively,22%,13%,4.5%,and 2%.The statistics of skynoise temperatures observed at different zenith angles under environmentswithout precipitation is also made.The results show that 80% of the observedsky noise temperatures at zenith angles of 10°,30°,50°and 70°are,respectively,in the ranges of 92-180K,39-52K,26-33K,and 21-27K.In addition,a comparison between surface rainfall rate recorded by theoptical raingauge and sky noise temperature measured by 19.5GHz radiometershows that the former lags behind the latter by about 5 minutes,implying non-uniform and inhomogeneous distribution of precipitation inthe air.In order to measure the precipitation aloft,the Chung-Li VHF radarwas operated simultaneously.Champaign observation shows that thereis no latency between sky noise temperature and VHF backscatter fromprecipitation.This result implies that the VHF backscatter from precipitationcan be employed to validate the observed sky noise temperature.Inaddition,we also find that the sky noise temperature may be as high as 155K(corresponding to 3.6dB attenuation)under an environment withoutsurface precipitation.This feature is attributed to the dense water vaporand heavy cloud.