Visible Infrared Spin Scan Radiometer Research Articles

Effects of joint assimilation of FY-4A AGRI and ground-based microwave radiometer on heavy rainfall prediction

As the latest generation of Chinese Geostationary Weather Satellites, Fengyun-4 carries the Advanced Geosynchronous Radiation Imager (AGRI), which has more spectral bands and higher temporal and spatial resolution than the Visible Infrared Spin-Scan Radiometer (VISSR) onboard geostationary satellite FY-2. Direct assimilation of the FY-4A AGRI datasets has been proved to be an efficient way to improve heavy rainfall simulation. We aim to assess the joint assimilation of AGRI infrared radiance and ground-based MWR (Microwave Radiometer) data on short-duration heavy rainfall prediction. RTTOV (Radiative Transfer for the TIROS Operational Vertical Sounder) is used as the observational operator for FY-4A AGRI data assimilation. The data assimilation interface is built in WRFDA 4.3 to achieve direct assimilation of FY4A AGRI radiance. The forecasting effectiveness of the joint assimilation for a typical heavy rainfall event over northern China is analyzed with four simulation experiments. The main conclusions are: 1) Assimilating MWR data can improve the initial humidity condition in the middle-lower layers, while AGRI radiance assimilation favors the initial humidity correction in the middle-upper layers. The joint assimilation of two datasets can remarkably improve the initial humidity condition in the entire column. 2) Data assimilation effectively improves the 6-h accumulated rainfall simulation. The joint assimilation of AGRI radiance and MWR data is superior to assimilating either of them. The joint assimilation significantly improves the rainfall forecast over the Beijing area, where the seven MWRs are distributed. 3) Data assimilation experiments present similar effects on predicted and initial humidity conditions. The MWR_DA experiment (only assimilate MWR data) markedly improves the humidity forecast in the middle-lower layers, while AGRI_DA (only assimilate AGRI data) is effective in the middle-upper layers. The joint assimilation of AGRI radiance and MWR data could skillfully correct the humidity distribution in the entire layers, allowing for more accurate heavy rainfall prediction. This paper provides a valuable basis for further improving the application of FY-4A AGRI radiance in numerical weather models.

Influence of inhomogeneous cloud fields on optical properties retrieved from satellite observations

Analyses of solar radiation exchanges between the atmosphere and clouds are vital for the understanding of climate processes and cycles. Comparisons of satellite‐to‐satellite or satellite‐to‐ground‐truth observations aiming at, elucidating the radiative behavior of atmospheric components (clouds, aerosols, gas, etc.), or validating data of a particular satellite are a common practice in global radiation investigations. In order to assess the quality of cloud optical properties derived from Geostationary Meteorological Satellite‐5/Stretched Visible Infrared Spin Scan Radiometer (GMS‐5/SVISSR), the former procedure (satellite‐to‐satellite comparison) was used. Data derived from GMS‐5/SVISSR satellite were compared with those from the polar‐orbiting Terra‐Moderate Resolution Imaging Spectroradiometer (Terra‐MODIS) satellite. This comparison showed serious discrepancies between cloud optical depth (COD) data retrieved from the two satellites' observations. GMS‐5/SVISSR‐retrieved COD appeared mostly lower than that of Terra‐MODIS. To understand the origin of such differences, an identification procedure of the major factors likely to affect these data is conducted. Some of these factors were the satellite viewing and solar conditions, the cloud thermodynamic phase differentiation and particle effective radius, and the cloud inhomogeneity. Then emphasis was put on the examination of the latter effect (i.e., the cloud inhomogeneity). The analysis procedure was as follows: First, data having close‐viewing geometries between both satellites were selected and used to understand the effects of the remaining factors. Among these, the cloud thermodynamic phase appeared to play the major role as analyses showed that most of the COD differences between both satellites were confined within ice clouds while warm clouds had the least discrepancies. This would suggest that the choice of a water cloud particle radiative transfer model to analyze a 2‐phase cloud radiation data, as used here, may produce large uncertainties in ice COD retrievals from at least one of the satellites. To avoid the cloud phase problem, a more restrictive data set comprising only water clouds (besides close‐viewing geometries between both satellites) was selected, and the impact of the degree of cloud inhomogeneity on the COD retrievals was evaluated. The study reveals that the 3‐D radiative effects deriving from the external cloud inhomogeneity, i.e., cloud asymmetry and structured sides, were the most influencing properties here. The GMS‐5/SVISSR interpretation of inhomogeneous cloud optical properties showed larger uncertainties than that of Terra‐MODIS. Furthermore, COD values of GMS‐5/SVISSR were systematically lower than those of Terra‐MODIS for the pixels at shadow sides of the cloud, while at illuminated sides they often showed higher values. For gentle or near‐plane‐parallel cloud surfaces, fewer discrepancies were noticed (the best agreement between both satellites' retrievals). At steep slopes of the shadow and illuminated cloud sides, GMS‐5/SVISSR average COD data were respectively under‐ and overestimated compared to those of Terra‐MODIS. COD differences between the two satellites could be sometimes higher than 30% for slopes steeper than 0.5 K/km.

A cross-calibration of GMS-5 thermal channels against ATSR-2

Motivated by the importance to weather and climate of the Indo-Pacific seas, we present a new calibration of the Visible Infrared Spin-Scan Radiometer (VISSR) on the geostationary meteorological satellite, GMS-5. VISSR imagery has significant potential for exploring the dynamics of the ocean and air–sea interactions in this poorly characterized region, by virtue of the VISSR's surface temperature retrieval capability and hourly sampling. However, the calibration of the thermal imagery supplied by the Japanese Meteorological Agency (JMA) is inconsistent with the spectral characteristics of the channels, and published details of the JMA calibration procedure are scant. We use the well-characterized Along-Track Scanning Radiometer 2 (ATSR-2) as a reference, and determine calibration corrections for GMS-5 VISSR. We obtain more credible VISSR brightness temperatures and demonstrate sea surface temperature (SST) retrieval that validates well against in situ measurements (bias ∼0.3 and scatter ∼0.4 K). Comparison with a widely used sea surface temperature analysis shows that the GMS-5 VISSR SST fields capture important spatial structure, absent in the analysis.

The Diurnal Cycle of Upper-Tropospheric Clouds Measured by GOES-VAS and the ISCCP

Abstract A comparison of diurnal cycles in high clouds (<440 hPa) measured by the Geostationary Operational Environmental Satellite Visible Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (GOES-VAS) and the International Satellite Cloud Climatology Project (ISCCP) was made. The GOES-VAS longwave infrared data allow uniform detection of upper-tropospheric cirrus clouds from daylight into night without effects from solar reflections. It is sensitive to thin cirrus, which are difficult to detect. But it is not available globally because the sounder instrument is flown only on geostationary satellites operated by the United States. The ISCCP, however, is a global dataset using five to seven geostationary satellites. Large diurnal cycles were found in the Rocky Mountains and along the northern coast of the Gulf of Mexico mainly in the summer season. In the Tropics substantial diurnal cycles also were found in central Brazil and the Atlantic ITCZ. In the winter over the continental United States, diur...

Analysis of Upper-Tropospheric Water Vapor Brightness Temperatures from SSM/T2, HIRS, and GMS-5 VISSR

Satellite microwave and infrared instruments sensitive to upper-tropospheric water vapor (UTWV) are compared using both simulated and observed cloud-cleared brightness temperatures (Tb’s). To filter out cloudy scenes, a cloud detection algorithm is developed for the Special Sensor Microwave/Temperature-2 (SSM/T2 or T2) data using the 92- and 150-GHz window channels. An analysis of the effect of clouds on the T2 183-GHz channels shows sensitivity primarily to high clouds containing ice, resulting in significantly better sampling of UTWV Tb’s over the convective zones and regions of persistent cloudiness. This is in contrast to the infrared sensors, which are extremely sensitive to any cloud contamination in the satellite field of view. A comparison of simulated UTWV Tb’s from T2, the High-resolution Infrared Sounder (HIRS), and the Visible Infrared Spin Scan Radiometer (VISSR) indicates a higher overall sensitivity to changes in UTWV in the T2 channel. HIRS and VISSR, however, are more sensitive to moisture at higher levels. Cloud-cleared Tb’s from T2 and HIRS were found to be highly correlated in the tropical dry zones and in regions of strong seasonal variability but less correlated at higher latitudes. The advantages of the microwave T2 sensor for monitoring UTWV are demonstrated by its greater sensitivity to changes in upper-tropospheric moisture and superior coverage over cloudy regions.

Satellite calibration using a collocated nadir observation technique: theoretical basis and application to the GMS-5 Pathfinder benchmark period

A collocated nadir observation technique has been used as part of the geostationary meteorological satellite (GMS) pathfinder project and is now employed at the Australian Bureau of Meteorology Research Centre to calibrate the visible infrared spin scan radiometer (VISSR) instrument used on GMS-5. It uses satellite-to-satellite cross calibration to bypass many of the problems inherent in the absolute calibration of satellite instruments. Orbital calculations determine where and when the VISSR and advanced very high resolution radiometer (AVHRR) instruments on the GMS and National Oceanic and Atmospheric Administration (NOAA) satellites, respectively, are observing the same Earth-atmosphere scene from the same direction at the same time. Results show that, with careful selection of calibration scenes, the satellites are observing the same radiation field, allowing a fundamental count-to-count calibration of the instrumentation. This calibration can subsequently be related to radiance. It should be possible to cross correlate all geostationary satellites currently employed using a similar method. This paper makes the following three contributions. 1) Using radiative transfer modeling, a sound theoretical basis for the calibration technique is provided. 2) Behavior of the GMS-5 VISSR instrument is tracked for the Pathfinder benchmark period (July 1, 1995-June 30, 1996). 3) Detailed theoretical and experimental comparison of the GMS-4 and GMS-5 VISSR instruments, which takes into account their different spectral response functions, is provided.

Improved Finite Impulse Response Filters for Enhanced Destriping of Geostationary Satellite Data

The visible infrared spin scan radiometer (VISSR) common to many geostationary satellites produces visible wavelength data contaminated with stripes. The stripes affect the usefulness of the data in quantitative studies. This paper briefly reviews the cause of the striping and then develops a tapered window finite impulse response (FIR) filter and a constrained least squares FIR filter. Both filters minimize the stripes in the visible data and simultaneously minimize any distortion in the filtered data. These new filters are also designed to minimize ringing near cloud edges—a problem often associated with earlier FIR filter designs used to remove striped noise in satellite data. Finally, the results obtained by using these new filtering methods are quantitatively compared with those produced by other destriping methods. Results from geostationary operational environment satellite (GOES-7) and the geostationary meteorological satellite (GMS-5) scenes show that both filters are superior to the other methods evaluated. Moreover, they are computationally efficient because they are implemented in the spatial domain. Significant differences between the noise structure of GOES-7 and GMS-5 visible data also are discussed; these differences appear not to be in the open literature. The new FIR filter designs can also be adapted for use with data taken with the improved VISSR-like instruments on the GOES-8 and GOES-9 satellites. The importance of proper destriping of geostationary satellite data for geophysical applications is discussed.

Calibration of GOES-VISSR, visible-band satellite data and its application to the analysis of a dust storm at Owens Lake, California

As part of a joint Russian/American dust-storm experiment, GOES-VISSR (Geostationary Operational Environmental Satellite, Visible-Infrared Spin-Scan Radiometer), data from a visible-band satellite image of a large dust storm emanating from Owens Lake, California were acquired on March 10 and 11, 1993. The satellite data were calibrated to targets of known ground reflectance factors and processed with radiative transfer techniques to yield aerosol (dust) optical depth at those stages of the dust storm when concurrent ground-based measurements of optical depth were made. Calibration of the satellite data is crucial for comparing surficial changes in remotely sensed data acquired over a period of time from the same area and for determining accurate concentrations of atmospheric aerosols using radiative transfer techniques. The calibration procedure forces the distribution of visible-band, DN (digital number) values, acquired on July 1, 1992, at 1731 GMT from the GOES-VISSR sensor over a large test area, to match the distribution of visible-band, DN values concurrently acquired from a Landsat MSS (Multispectral Scanner) sensor over the same test area; the Landsat MSS DN values were directly associated with reflectance factors measured from ground targets. The calibrated GOES-VISSR data for July 1, 1992, were then used to calibrate other GOES-VISSR data acquired on March 10 and 11, 1993, during the dust storm. Uncertainties in location of ground targets, bi-directional reflectance and atmospheric attenuation contribute an error of approximately ±0.02 in the satellite-inferred ground reflectance factors. On March 11 at 1031 PST the satellite-received radiances during the peak of the storm were 3 times larger than predicted by our radiative transfer model for a pure clay dust plume of infinite optical depth. This result supported ground-based measurements that the plume at that time was composed primarily of large salt grains, probably sodium sulfate, which could not be properly characterized in our radiative transfer model. Further, the satellite data showed that the salt fell out of the plume within 35 km from the source. Finer-grained, clay dust was observed to extend beyond the salt-laden plume and was the major component of the dust plume after 1131 PST, when erosion of the salt crust on Owens Lake ceased. By 1331 and 1401 PST satellite-inferred, optical depths compared favorably with measurements concurrently acquired at the ground. Uncertainties in bi-directional reflectance, atmospheric attenuation, and locating ground points in the satellite data manifest errors between the inferred and measured optical depths in the range of 20 to 50%; these errors would be much greater without the calibration of the GOES-VISSR data. Changes in satellite-inferred reflectance factors over the lake bed during the course of the storm showed that 76 km 2 of the surface was disrupted during the March 11 storm, suggesting as much as 76 × 10 3 m 3 of crustal material were displaced for each millimeter of several estimated to have been moved during the storm; an unknown fraction of the displaced material was suspended. The satellite data also showed dust fallout on mountain snowfields. Whereas fallout may have removed most of the salt, satellite data acquired at 1631 PST, when the plume had a large brightness contrast with the ground, showed that it covered over 2500 km 2 and contained at least 1.6 × 10 9 g of sediment. For such a small source area, the dust represents a substantial contribution to the regional and global load of aerosols.

A Comparison of Saturation Pressure Differences and GOES VAS Estimates to Surface Observations of Cloudiness

Saturation pressure differences are calculated from upper-air soundings and compared to manual surface observations of cloudiness. The mean saturation pressure difference between 1000 and 700, 700 and 400, and 400 and 300 mb is calculated and compared to the observed composite cloudiness for those layers. Results indicate that as the absolute value of saturation pressure difference decreases toward zero, the resulting ground observed composite cloud amount increases. However, the mean saturation pressure difference for high clouds ranges from 64 mb under clear skies to 16 mb for overcast conditions. This corresponds to relative humidities between 25% and 76%. Most previous studies do not indicate such large cloud amounts at these humidities. Three empirical relationships that define low, middle, and high clouds are developed based on one year of comparisons. These relationships are then tested on an independent dataset that include a wide variety of cloud cover conditions. Qualitative comparisons are made to manual observations of cloudiness and indicate that the relationships overall slightly overestimate the frequency of cloudiness. Cloudiness derived from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the Geostationary Environmental Operational Satellite 7 using the CO{sub 2} slicing technique is also compared to surface observations. Results indicate thatmore » the satellite-derived cloudiness overestimates cloudiness compared with surface observations but is also very similar to the saturation pressure difference estimates. 12 refs., 13 figs., 3 tabs.« less

Satellite-Model Coupled Analysis of Convective Potential in Florida with VAS Water Vapor and Surface Temperature Data

Abstract A system for time-continuous mesoscale weather analysis is applied to a study of convective cloud development in central Florida. The analysis system incorporates water vapor concentrations and surface temperatures retrieved from infrared VISSR (Visible–Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) satellite data, with coupling between the retrieval process and time integration of a mesoscale model. Analyses prepared with variations of this coupled system are compared with a control numerical analysis prepared with only conventional meteorological observations and are validated against surface and upper-air data collected for the Convection and Precipitation/Electrification experiment. The coupled analyses assimilate six sets of VAS data over an 8-h period on 19 July 1991 and depict water vapor gradients at far greater horizontal resolution than is available from conventional observations and with an overall accuracy better than the control analysis. The coupled system's ability to ass...

Cloudiness and Its Relationship to Saturation Pressure Differences during a Developing East Coast Winter Storm

Cloudiness derived from surface observations and the Geostationary Operational Environmental Satellite VISSR (Visible–Infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) are compared with thermodynamic properties derived from upper-air soundings over the Gulf Stream locale during a developing winter storm. The Gulf Stream locale covers the United States mid-Atlantic coastal states, the Gulf Stream, and portions of the Sargasso Sea. Cloudiness is found quite frequently in this region. Cloud-top pressures are derived from VAS using the CO2 slicing technique and a simple threshold procedure. Cloud-base heights and cloud fractions are obtained from National Weather Service hourly reporting stations. The saturation pressure differences, defined as the difference between air parcel pressure and saturation-level pressure (lifted condensation level), are derived from upper-air soundings. Collocated comparisons with VAS and surface observations are also made. Results indicate that cloudiness is observed nearly all of the time during the 6-day period, well above the 8-yr mean. High, middle, and low opaque cloudiness are found approximately equally. Furthermore, of the high- and midlevel cloudiness observed, a considerable amount is determined to be semitransparent to terrestrial radiation. Comparisons of satellite-inferred cloudiness with surface observations indicate that the satellite can complement surface observations of cloud cover, particularly above 700 mb. Surface-observed cloudiness is segregated according to a composite cloud fraction and compared to the mean saturation pressure difference for a 1000–600-mb layer. The analysis suggests that this conserved variable may be a good indicator for estimating cloud fraction. Large negative values of saturation pressure difference correlate highly with clear skies, while those approaching zero correlate with overcast conditions. Scattered and broken cloud fractions are associated with increasing values of the saturation pressure difference. Furthermore, cloud fractions observed in this study are considerably higher than those reported in similar studies and by other cloud fraction formulations.

A Method for Multisensor-Multispectral Satellite Data Fusion

Abstract Multisensor-multispectral scientific data applications require a tremendous investment regarding data preparation and analysis. A data fusion method is developed that is general enough for use with any scan-line-based datasets (satellite and ground based) and enables multisensor-multispectral datasets to be merged on a routine basis. In particular, advanced software processing techniques in the Polar Orbiter Remapping and Transformation Application Library (PORTAL) are used to show how polar (e.g., Special Sensor Microwave/Imager data from DMSP) and geostationary data (e.g., Visible-Infrared Spin Scan Radiometer data from GOES) can be spatially combined routinely in an efficient manner. The PORTAL system can also be used to combine data from sensors on the same satellite that have radically different earth scan patterns and ground resolutions. A self-describing, generalized data format is used to modularize the data processing flow and obtain significant improvements in terms of flexibility, exte...

Diurnal Variations in Cloud Frequency over the Gulf Stream Locale

Abstract This paper documents evidence of a diurnal variability in cloudiness over the Gulf Stream locale. The Gulf Stream locale (GSL) is defined as the region covering 31°–38°N, 82°–71°W. The Gulf Stream, which occupies a portion of the GSL, is a warm current of water that flows south to north along the east coast of the United States and provides conditions conducive for the development of cloudiness. Cloud heights derived from the GOES VISSR (Visible-infrared Spin Scan Radiometer) Atmospheric Sounder (VAS) are obtained and used to produce a 7-yr climatology of the diurnal variation in the frequency of low-, middle-,and high-level cloudiness. The climatology is segregated into summer and winter seasons. Diurnal variations are found during the summer and winter. Satellite observations over land indicate a maximum in the frequency of low cloudiness during daytime and a minimum at night. In addition, high cloudiness is found to increase significantly late in the afternoon and evening. Over the Gulf Stream...

Clustering of Satellite Sounding Radiances to Investigate Intense Low-Level Humidity Gradients

Abstract Satellite-derived profiles of temperature and dewpoint (retrievals) are obtained using radiance data from the Visible-infrared Spin Scan Radiometer Atmospheric Sounder. Individual fields of view that are input to the retrieval algorithm must be horizontally averaged to provide suitable signal-to-noise ratios. This paper investigates three methods for performing this averaging: 1)a blocking approach that is employed operationally, 2) a manual procedure that seeks to maximize atmospheric gradients, and 3) an objective procedure called clustering that takes advantage of similarities in satellite measurements to avoid smearing the gradient information. The three techniques are examined on 10&amp;#x96;11 July 1989 when intense gradients of humidity were present over the Florida peninsula. Results show that the clustering scheme produced retrievals that were very similar to those obtained manually. Both schemes indicated strong humidity gradients in the lower troposphere. The blocking procedure produced less intense gradients. The retrieval information is used to examine conditions leading to fair weather on 10 July but intense thunderstorm development on 11 July.

The Retrieval of Marine Stratiform Cloud Properties from Multiple Observations in the 3.9-µm Window under Conditions of Varying Solar Illumination

Abstract Radiometric observations in the 3.9-µm region have been used by a number of investigators for the determination of cloud parameters or sea surface temperature at night. Only a few attempts have been made to perform quantitative assessments of cloud and surface properties during the daytime because of the inability to distinguish between the thermal and solar components of the satellite-sensed radiances. This paper presents a new method of separating the thermal and solar components of upwelling 3.9-µm radiances. Two collocated satellite observations are made under conditions where the solar illumination angle changes but the thermal structure of the cloud and atmosphere, as well as the cloud microphysics change very little. These conditions can easily be met by observing the same cloud from geosynchoronous orbit over a short time interval during the morning hours. When the radiances are differenced under these constraints, the thermal components cancel, and the difference in the radiances is simply the difference in the solar component. With a few simplifying assumptions, a cloud microphysical property, specifically effective radius, can be inferred. This parameter is of particular importance to both climate modeling and global change studies. The methodology developed in this paper is applied to data from the Visible-Infrared Spin Scan Radiometer Atmospheric Sounder onboard the GOES-7 spacecraft for a period in August 1992.

Trends in South American biomass burning detected with the GOES visible infrared spin scan radiometer atmospheric sounder from 1983 to 1991

In an effort to get a better understanding of the extent and patterns of burning in South America, geostationary satellite data have been used to monitor active fires. Previous work demonstrated the ability to manually detect subpixel fire activity in selected areas of the selva and cerrado regions in South America with shortwave and longwave infrared data available from the Geostationary Operational Environmental Satellite (GOES) visible infrared spin scan radiometer atmospheric sounder (VAS) This paper presents the GOES VAS automated biomass‐burning algorithm (ABBA) which was developed to determine basin‐wide trends in fire activity in South America utilizing the GOES VAS archive. Comparisons between the manual and the automated techniques revealed that overall, the ABBA proved to be more consistent in identifying fires and better suited for trend analysis. The automated algorithm was applied daily to a study area extending from 5°S to 15°S and from 45°W to 70°W for 2 weeks at the peak of the burning seasons in South America in 1983, 1988, 1989, and 1991 in an effort to measure the areal extent of burning in South America during the past decade and to provide additional insight into the diurnal signature in satellite detection of biomass‐burning activities. The expansion of the regions of burning are readily detected in a comparison of these 4 years. From 1983 to 1991 the amount of burning detected by the GOES VAS ABBA during these 2‐week periods nearly doubled in the selva and mixed regions and tripled in the cerrado. Diurnal analyses confirmed earlier results indicating that the optimum time to monitor biomass burning is around 1530 UTC.

A Comparison of Ground and Satellite Observations of Cloud Cover

Abstract A processing scheme that determines cloud height and amount based on radiances from the Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) using a CO2 absorption technique has been installed on the National Environmental Satellite Data and Information Service VAS Data Utilization Center computer system in Washington, D.C. The processed data will complement the Automated Surface Observing System (ASOS). ASOS uses automated ground equipment that provides near-continuous observations of surface weather data that are currently manually obtained. Geostationary multispectral infrared measurements are available every hour with information on clouds above the ASOS laser ceilometer viewing limit of 12 000 ft. The combined ASOS/satellite system will be able to depict cloud conditions at all levels up to 50 000 ft. The error rate of combined ASOS and satellite observations is less than 4% of the total sample in a comparison test with manual observations performed by National Weather Service per...

Degradation of the VISSR Visible Sensor onGMS-3during June 1987–December 1988

Abstract Degradation of the VISSR (Visible-Infrared Spin Scan Radiometer) visible sensor on the GMS-3 is estimated for a period from June 1987 to December 1988 by monitoring reflectances obtained from four targets on the earth. Samples of the highest brightness of midday cloud images and albedos observed over three desert target areas (the Great Sandy Desert, the Taklamakan Desert, and the Gobi Desert) are employed as targets. The results show that the brightness measured by the satellite sensor had appreciably deteriorated during the study period. The rate of degradation is estimated to be 5.3% per year from the analysis of the highest brightness, and 3.7%, 3.7%, and 5.0% for the case of the Great Sandy Desert, the Taklamakan Desert, and the Gobi Desert, respectively. For the average of four cases, the estimated rate of degradation is 4.4% per year.

Geostationary satellite detection of bio mass burning in South America

Abstract This paper presents the results of using Geostationary Operational Environmental Satellite (GOES) Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) data to monitor biomass burning associated with deforestation and grassland management in South America. The technique of Matson and Dozier has been adapted to GOES VAS short-wave and long-wave infrared window data to determine ihe size and temperature of fires associated with these activities. Although VAS data do not offer the spatial resolution available with Advanced Very High Resolution Radiometer (AVHRR) data (7 km versus I km) this decreased resolution does not seem to hinder the ability of the VAS instrument to delect fires; in some cases it proves to be advantageous, in that saturation does not occur as often. Sequences of VAS visible data are helpful in verifying that the hot spots sensed in the infrared are actually related to fires. Furthermore, the smoke of the fires can be tracked in time to determine their motion and traje...

Comparison of Column Water Vapor Measurements Using Downward-looking Near-Infrared and Infrared Imaging Systems and Upward-looking Microwave Radiometers

Remote soundings of precipitable water vapor from three systems are compared with each other and with ground truth from radiosondes. Ancillary data from a mesoscale network of surface observing stations and from wind-profiling radars are also used in the analysis. The three remote-sounding techniques are: (a) a reflectance technique using spectral data collected by the Airborne Visible-Infrared Imaging Spectrometer; (b) an emission technique using Visible-Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) data acquired from the NOAA's GOES; and (c) a microwave technique using data from a limited network of three ground-based dual-channel microwave radiometers. The data were taken over the Front Range of eastern Colorado on 22-23 March 1990. The generally small differences between the three types of remote-sounding measurements are consistent with the horizontal and temporal resolutions of the instruments. The microwave and optical reflectance measurements agreed to within 0.1 cm; comparisons of the microwave data with radiosondes were also either as good or explainable. The largest differences between the VAS and the microwave radiometer at Elbert were between 0.4 and 0.5 cm and appear to be due to variable terrain within the satellite footprint.