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Sundar A Christopher - One of the best experts on this subject based on the ideXlab platform.
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GOES 8 aerosol optical thickness assimilation in a mesoscale model online integration of aerosol radiative effects
Journal of Geophysical Research, 2004Co-Authors: Jun Wang, U S Nair, Sundar A ChristopherAbstract:[1] To investigate the importance of aerosol radiative effects in the troposphere, numerical simulation of a dust event during the Puerto Rico Dust Experiment is presented by using the Colorado State University Regional Atmospheric Modeling System (RAMS). Through assimilation of geostationary satellite-derived aerosol optical thickness (AOT) into the RAMS, spatial and temporal aerosol distribution is optimally characterized, facilitating direct comparison with surface observations of downwelling radiative energy fluxes and 2 m air temperature that is not possible with a free-running mesoscale model. Two simulations with and without consideration of aerosol radiative effects are performed. Comparisons against observations show that direct online integration of aerosol radiative effects produces realistic downwelling shortwave and longwave fluxes at the surface but minimal improvement on 2 m air temperature at the observation location. Numerical simulations show that for the dust loading considered in this study (AOT = 0.45 at 0.67 μm), if the dust radiative effects are not properly represented, the uncertainty in the simulated AOT is about ±5 to ±10%, the surface radiative energy is overestimated by 30–40 W m−2 during the day and underestimated by 10 W m−2 during the night, and the bias in air temperatures near the surface could be up to ±0.5°C, though these biases also depend on local time, AOT values, and surface properties. The results from this study demonstrate that the assimilation of satellite aerosol retrievals not only improves the aerosol forecasts but also has the potential to reduce the uncertainties in modeling the surface energy budget and other associated atmospheric processes.
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GOES 8 retrieval of dust aerosol optical thickness over the atlantic ocean during pride
Journal of Geophysical Research, 2003Co-Authors: Jun Wang, Sundar A Christopher, Jeffrey S Reid, Hal Maring, Dennis L Savoie, B N Holben, J M Livingston, Philip B Russell, Shikeng YangAbstract:[1] Using 30 days of half-hourly, high temporal resolution GOES 8 imager data and radiative transfer calculations, dust aerosol optical thickness (AOT) was retrieved over the Atlantic Ocean (14� N � 26� N, 73� W–63� W) during the Puerto Rico Dust Experiment (PRIDE). Dust aerosol size distributions and complex index of refraction inferred from ground-based measurements (1.53–0.0015i at 0.55 mm), which were used in Mie calculations and a plane-parallel discrete ordinate radiative transfer model (DISORT) to compute look up tables for AOT retrievals. Using a combination of spectral, spatial, and temporal tests, a dust detection algorithm was developed from the GOES 8 imager data. The degradation of the signal response relative to the prelaunched calibration of the GOES 8 visible channel was 39% in July 2000 and the GOES 8 AOT detection limit was estimated to be 0.04 in AOT (0.67 mm). The satellite-retrieved AOT were then compared with AOT values derived from ground-based Sun photometer (SP) sites. The comparison showed that GOES 8 retrieved AOT are in good agreement with the SP derived values, with linear correlation coefficient of 0.91 and 0.80 for the two sites. The GOES 8 monthly mean 0.67 mm AOT (0.19 ± 0.13, 0.22 ± 0.12) over the two SP sites matched the monthly mean SPAOT values (0.23 ± 0.13, 0.22 ± 0.10). The linear correlation between the GOES 8 retrieved AOT and the aircraft derived values from particle probe data and airborne Sun photometer AATS-6 measurements were 0.88 and 0.83, respectively. Besides the uncertainties from the nonspherical effect of dust aerosols, sensitivity studies showed that the uncertainties (t) of the GOES 8 retrieved AOT values were mainly from the uncertainties due to the imaginary part of refractive index (t = ±0.05) and surface reflectance [t = ±(0.02 � 0.04)]. This paper demonstrates the application of geostationary satellites to detect and retrieve dust AOT even at low to moderate AOTs. The GOES 8 imager with high temporal resolutions also captures aerosol diurnal variation in this study that can further reduce the uncertainties in the current aerosol forcing estimations caused by the high temporal variations of AOT, thereby playing a complementary role with global AOT retrievals from polar orbiting satellites. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: dust aerosol, diurnal optical depth, GOES 8, radiative forcing
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GOES 8 retrieval of dust aerosol optical thickness over the atlantic ocean during pride puerto rico dust experiment pride1
Journal of Geophysical Research, 2003Co-Authors: Jun Wang, Sundar A Christopher, Jeffrey S Reid, Hal Maring, Dennis L Savoie, B N Holben, J M Livingston, Philip B Russell, Shikeng YangsAbstract:Using 30 days of half-hourly, high temporal resolution GOES 8 imager data and radiative transfer calculations, dust aerosol optical thickness (AOT) was retrieved over the Atlantic Ocean (14°N ∼ 26°N, 73°W-63°W) during the Puerto Rico Dust Experiment (PRIDE). Dust aerosol size distributions and complex index of refraction inferred from ground-based measurements (1.53-0.0015i at 0.55 μm), which were used in Mie calculations and a plane-parallel discrete ordinate radiative transfer model (DISORT) to compute look up tables for AOT retrievals. Using a combination of spectral, spatial, and temporal tests, a dust detection algorithm was developed from the GOES 8 imager data. The degradation of the signal response relative to the prelaunched calibration of the GOES 8 visible channel was 39% in July 2000 and the GOES 8 AOT detection limit was estimated to be 0.04 in AOT (0.67 μm). The satellite-retrieved AOT were then compared with AOT values derived from ground-based Sun photometer (SP) sites. The comparison showed that GOES 8 retrieved AOT are in good agreement with the SP derived values, with linear correlation coefficient of 0.91 and 0.80 for the two sites. The GOES 8 monthly mean 0.67 μm AOT (0.19 ± 0.13, 0.22 ± 0.12) over the two SP sites matched the monthly mean SP AOT values (0.23 ± 0.13, 0.22 ± 0.10). The linear correlation between the GOES 8 retrieved AOT and the aircraft derived values from particle probe data and airborne Sun photometer AATS-6 measurements were 0.88 and 0.83, respectively. Besides the uncertainties from the nonspherical effect of dust aerosols, sensitivity studies showed that the uncertainties (Δτ) of the GOES 8 retrieved AOT values were mainly from the uncertainties due to the imaginary part of refractive index (Δτ = ±0.05) and surface reflectance [Δτ = ±(0.02 ∼ 0.04)]. This paper demonstrates the application of geostationary satellites to detect and retrieve dust AOT even at low to moderate AOTs. The GOES 8 imager with high temporal resolutions also captures aerosol diurnal variation in this study that can further reduce the uncertainties in the current aerosol forcing estimations caused by the high temporal variations of AOT, thereby playing a complementary role with global AOT retrievals from polar orbiting satellites.
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daytime variation of shortwave direct radiative forcing of biomass burning aerosols from GOES 8 imager
Journal of the Atmospheric Sciences, 2002Co-Authors: Sundar A Christopher, Jianglong ZhangAbstract:Hourly Geostationary Operational Environmental Satellite-8 (GOES-8)imager data (1344‐1944 UTC) from 20 July‐31 August 1998 were used to study the daytime variation of shortwave direct radiative forcing (SWARF) of smoke aerosols over biomass burning regions in South America (48‐168S, 518‐658W). Vicarious calibration procedures were used to adjust the GOES visible channel reflectance values for the degradation in signal response. Using Mie theory and discrete ordinate radiative transfer (DISORT) calculations, smoke aerosol optical thickness (AOT) was estimated at 0.67 mm. The GOES-retrieved AOT was then compared against ground-based AOT retrieved values. Using the retrieved GOES-8 AOT, a four-stream broadband radiative transfer model was used to compute shortwave fluxes for smoke aerosols at the top of the atmosphere (TOA). The daytime variation of smoke AOT and SWARF was examined for the study area. For selected days, the Clouds and the Earth’s Radiant Energy System (CERES) TOA shortwave (SW) fluxes are compared against the model-derived SW fluxes. Results of this study show that the GOES-derived AOT is in excellent agreement with Aerosol Robotic Network (AERONET)-derived AOT values with linear correlation coefficient of 0.97. The TOA CERES-estimated SW fluxes compare well with the model-calculated SW fluxes with linear correlation coefficient of 0.94. For August 1998 the daytime diurnally averaged AOT and SWARF for the study area is 0.63 6 0.39 and 245.8 6 18.8 W m22, respectively. This is among the first studies to estimate the daytime diurnal variation of SWARF of smoke aerosols using satellite data.
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GOES 8 and noaa 14 avhrr retrieval of smoke aerosol optical thickness during scar b
International Journal of Remote Sensing, 2002Co-Authors: Sundar A Christopher, B N Holben, Jianglong Zhang, S K YangAbstract:Using the NOAA-14 1-km Advanced Very High Resolution Radiometer (AVHRR) and the Geostationary Operational Environmental Satellite (GOES-8) imager data, smoke aerosol optical thickness ( ) is retrieved over land during the Smoke, Clouds and Radiation-Brazil (SCAR-B) experiment in Brazil during August-September 1995. The satellite-retrieved values are then compared against ground-based sunphotometer derived values from the Aerosol Robotic Network (AERONET) program. Both the AVHRR and GOES-8 retrieved values are in excellent agreement with the AERONET derived values with linear correlation coefficients of 0.93. A single scattering albedo of 0.90 (at 0.67 w m) provides the best fit between the GOES-8 and AERONET values. The sensitivity of the retrieved to assumed surface albedo and aerosol single scattering albedo are also examined. A simple multi-spectral thresholding algorithm is used to separate smoke from other features from GOES-8 satellite imagery and regional maps of are provided. Our r...
Kenneth R Knapp - One of the best experts on this subject based on the ideXlab platform.
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gridded satellite gridsat GOES and conus data
Earth System Science Data, 2018Co-Authors: Kenneth R Knapp, Scott L WilkinsAbstract:Abstract. The Geostationary Operational Environmental Satellite (GOES) series is operated by the US National Oceanographic and Atmospheric Administration (NOAA). While in operation since the mid-1970s, the current series (GOES 8–15) has been operational since 1994. This document describes the Gridded Satellite (GridSat) data, which provide GOES data in a modern format. Four steps describe the conversion of original GOES data to GridSat data: (1) temporal resampling to produce files with evenly spaced time steps, (2) spatial remapping to produce evenly spaced gridded data (0.04 ∘ latitude), (3) calibrating the original data and storing brightness temperatures for infrared (IR) channels and reflectance for the visible channel, and (4) calculating spatial variability to provide extra information that can help identify clouds. The GridSat data are provided on two separate domains: GridSat-GOES provides hourly data for the Western Hemisphere (spanning the entire GOES domain) and GridSat-CONUS covers the contiguous US (CONUS) every 15 min (dataset reference: https://doi.org/10.7289/V5HM56GM ).
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toward aerosol optical depth retrievals over land from GOES visible radiances determining surface reflectance
International Journal of Remote Sensing, 2005Co-Authors: Kenneth R Knapp, Robert Frouin, Shobha Kondragunta, Ana I PradosAbstract:Frequent observations of aerosol over land are desirable for aviation, air pollution and health applications. Thus, a method is proposed here to correct surface effects and retrieve aerosol optical depth using visible reflectance measurements from the Geostationary Operational Environmental Satellite (GOES). The surface contribution is determined from temporal compositing of visible imagery, where darker pixels correspond to less atmospheric attenuation and surface reflectance is deduced from the composite using radiative transfer. The method is applied to GOES‐8 imagery over the eastern US. Retrieved surface reflectance is compared with separate retrievals using a priori ground‐based observations of aerosol optical depth. The results suggest that surface reflectances can be determined to within ±0.04. The composite‐derived surface reflectance is further analysed by retrieving aerosol optical depth and validating retrievals with Aerosol Robotic Network (AERONET) observations. This analysis indicates that ...
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quantification of aerosol signal in GOES 8 visible imagery over the united states
Journal of Geophysical Research, 2002Co-Authors: Kenneth R KnappAbstract:[1] Changes in the top-of-the-atmosphere reflectance due to variations in the aerosol optical depth (τ) make retrieving τ from satellite possible. This aerosol signal is greatest for non-absorbing aerosol over dark surfaces and is least (often less than zero) for absorbing aerosols over bright surfaces. In general, previous aerosol retrieval research has been in regions where the signal is known to be large, for example, aerosol over ocean or biomass burning over heavily vegetated land. This study, however, looks at the aerosol signal and its variation over North America to determine when and where τ retrieval is possible. The results show that the aerosol signal is sufficiently large for τ retrieval over most of the sites studied; exceptions are located in the southwestern United States where the surface reflectance is large. Further, this aerosol signal closely corresponds with radiative transfer simulations, which suggests that aerosol optical depth retrieval over North America and the adjoining oceans is possible from geostationary orbit. The implication is that timely (e.g., 30 min intervals) observations of aerosol are possible. Such observations could aid research efforts in pollutant transport, air quality forecasting, and wildfire monitoring.
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aerosol optical depth retrieval from GOES 8 uncertainty study and retrieval validation over south america
Journal of Geophysical Research, 2002Co-Authors: Kenneth R Knapp, Thomas Vonder H Haar, Yoram J KaufmanAbstract:[1] An algorithm for aerosol optical depth τ retrieval from the Geostationary Observational Environmental Satellite (GOES) series is described, where the darkest pixels are used to create a spatial composite of surface reflectance. The data are calibrated and corrected for atmospheric extinction to retrieve the surface reflectance which is then used to retrieved τ. Analysis suggests that τ retrieval uncertainty is ±18–34% depending on the certainty of the assumed radiative transfer model parameters. Retrieval uncertainty is less over low surface reflectances and at large scattering angles. The retrieval algorithm is validated against Sun-sky radiometer τ measurements for aerosols emitted by biomass burning in South America during 1995 and 1998. The relative differences between observed and retrieved τ are within the estimated uncertainty, having correlations ranging from 0.78 to 0.97. Further, the GOES retrievals are compared to τ retrieved using the Moderate-Resolution Imaging Spectroradiometer (MODIS) airborne simulator (MAS). The average relative difference in this comparison is 11%, thus retrieval validations are again within the estimated algorithm uncertainty. These results suggest that the GOES satellite can be used to monitor aerosols over land, while the agreement between MAS and GOES retrievals suggests the ability to combine the spectral abilities of MODIS with the temporal observations of GOES.
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calibration of the eighth geostationary observational environmental satellite GOES 8 imager visible sensor
Journal of Atmospheric and Oceanic Technology, 2000Co-Authors: Kenneth R Knapp, Thomas Vonder H HaarAbstract:Abstract The GOES-8/Imager has provided scientifically valuable imagery since its launch in April of 1994. However, without an onboard calibration source most research applications involving its data have been limited to qualitative analysis of the imagery. Presented herein is a review of previous quantitative work, including the prelaunch calibration information, and results of a new calibration effort that compares GOES-8/Imager raw counts of clear ocean scenes to theoretical satellite-detected radiance values from a radiative transfer model. Monthly averages of the calibration coefficient are presented at 6-month intervals from August 1995 through August 1999. Although the technique differs from previous calibration efforts, which compare Geostationary Operational Environmental Satellite observations to some reference instrument, the new calibration results agree well with previous results. The calibration suggests a one-time decrease of 7.6% shortly after launch, and an ongoing annual degradation of 5...
Ronald L Johnson - One of the best experts on this subject based on the ideXlab platform.
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hailstorm damage observed from the GOES 8 satellite the 5 6 july 1996 butte meade storm
Monthly Weather Review, 1998Co-Authors: Brian A Klimowski, Mark R Hjelmfelt, Matthew J Bunkers, Don Sedlacek, Ronald L JohnsonAbstract:Late in the evening of 5 July 1996, a supercell thunderstorm developed near the Montana–Wyoming–South Dakota border and moved to the southeast across western South Dakota. This storm was particularly notable for its persistent combination of large hail and extremely strong winds, which caused almost complete vegetative defoliation and destruction within a 120-km-long path. So extensive was the impact of the storm (especially in Butte and Meade counties of South Dakota) that the vegetation scar was visible for over a month on Geostationary Operational Environmental Satellite-8 (GOES-8) visible satellite imagery. This article briefly describes the nature of this extreme local storm event (hereafter referred to as the Butte–Meade storm) and the conditions responsible for creating the satellite-observed damage swath.
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picture of the month hailstorm damage observed from the GOES 8 satellite the 5 6 july 1996 butte meade storm
1998Co-Authors: Brian A Klimowski, Mark R Hjelmfelt, Matthew J Bunkers, Don Sedlacek, Ronald L JohnsonAbstract:1. IntroductionLate in the evening of 5 July 1996, a supercell thun-derstorm developed near the Montana–Wyoming–SouthDakota border and moved to the southeast across west-ern South Dakota. This storm was particularly notablefor its persistent combination of large hail and extremelystrong winds, which caused almost complete vegetativedefoliation and destruction within a 120-km-long path.So extensive was the impact of the storm (especially inButte and Meade counties of South Dakota) that thevegetation scar was visible for over a month on Geo-stationary Operational Environmental Satellite-8(GOES-8) visible satellite imagery. This article brieflydescribes the nature of this extreme local storm event(hereafter referred to as the Butte–Meade storm) andthe conditions responsible for creating the satellite-ob-served damage swath.2. DiscussionThe GOES-8visible satellite images from before (28June) and after (15 July) the 5–6 July 1996 Butte–Meadestorm illustrate the surface damage from this event (Fig.1). The damaged areas are apparent in the 15 July image
B N Holben - One of the best experts on this subject based on the ideXlab platform.
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GOES 8 retrieval of dust aerosol optical thickness over the atlantic ocean during pride
Journal of Geophysical Research, 2003Co-Authors: Jun Wang, Sundar A Christopher, Jeffrey S Reid, Hal Maring, Dennis L Savoie, B N Holben, J M Livingston, Philip B Russell, Shikeng YangAbstract:[1] Using 30 days of half-hourly, high temporal resolution GOES 8 imager data and radiative transfer calculations, dust aerosol optical thickness (AOT) was retrieved over the Atlantic Ocean (14� N � 26� N, 73� W–63� W) during the Puerto Rico Dust Experiment (PRIDE). Dust aerosol size distributions and complex index of refraction inferred from ground-based measurements (1.53–0.0015i at 0.55 mm), which were used in Mie calculations and a plane-parallel discrete ordinate radiative transfer model (DISORT) to compute look up tables for AOT retrievals. Using a combination of spectral, spatial, and temporal tests, a dust detection algorithm was developed from the GOES 8 imager data. The degradation of the signal response relative to the prelaunched calibration of the GOES 8 visible channel was 39% in July 2000 and the GOES 8 AOT detection limit was estimated to be 0.04 in AOT (0.67 mm). The satellite-retrieved AOT were then compared with AOT values derived from ground-based Sun photometer (SP) sites. The comparison showed that GOES 8 retrieved AOT are in good agreement with the SP derived values, with linear correlation coefficient of 0.91 and 0.80 for the two sites. The GOES 8 monthly mean 0.67 mm AOT (0.19 ± 0.13, 0.22 ± 0.12) over the two SP sites matched the monthly mean SPAOT values (0.23 ± 0.13, 0.22 ± 0.10). The linear correlation between the GOES 8 retrieved AOT and the aircraft derived values from particle probe data and airborne Sun photometer AATS-6 measurements were 0.88 and 0.83, respectively. Besides the uncertainties from the nonspherical effect of dust aerosols, sensitivity studies showed that the uncertainties (t) of the GOES 8 retrieved AOT values were mainly from the uncertainties due to the imaginary part of refractive index (t = ±0.05) and surface reflectance [t = ±(0.02 � 0.04)]. This paper demonstrates the application of geostationary satellites to detect and retrieve dust AOT even at low to moderate AOTs. The GOES 8 imager with high temporal resolutions also captures aerosol diurnal variation in this study that can further reduce the uncertainties in the current aerosol forcing estimations caused by the high temporal variations of AOT, thereby playing a complementary role with global AOT retrievals from polar orbiting satellites. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; KEYWORDS: dust aerosol, diurnal optical depth, GOES 8, radiative forcing
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GOES 8 retrieval of dust aerosol optical thickness over the atlantic ocean during pride puerto rico dust experiment pride1
Journal of Geophysical Research, 2003Co-Authors: Jun Wang, Sundar A Christopher, Jeffrey S Reid, Hal Maring, Dennis L Savoie, B N Holben, J M Livingston, Philip B Russell, Shikeng YangsAbstract:Using 30 days of half-hourly, high temporal resolution GOES 8 imager data and radiative transfer calculations, dust aerosol optical thickness (AOT) was retrieved over the Atlantic Ocean (14°N ∼ 26°N, 73°W-63°W) during the Puerto Rico Dust Experiment (PRIDE). Dust aerosol size distributions and complex index of refraction inferred from ground-based measurements (1.53-0.0015i at 0.55 μm), which were used in Mie calculations and a plane-parallel discrete ordinate radiative transfer model (DISORT) to compute look up tables for AOT retrievals. Using a combination of spectral, spatial, and temporal tests, a dust detection algorithm was developed from the GOES 8 imager data. The degradation of the signal response relative to the prelaunched calibration of the GOES 8 visible channel was 39% in July 2000 and the GOES 8 AOT detection limit was estimated to be 0.04 in AOT (0.67 μm). The satellite-retrieved AOT were then compared with AOT values derived from ground-based Sun photometer (SP) sites. The comparison showed that GOES 8 retrieved AOT are in good agreement with the SP derived values, with linear correlation coefficient of 0.91 and 0.80 for the two sites. The GOES 8 monthly mean 0.67 μm AOT (0.19 ± 0.13, 0.22 ± 0.12) over the two SP sites matched the monthly mean SP AOT values (0.23 ± 0.13, 0.22 ± 0.10). The linear correlation between the GOES 8 retrieved AOT and the aircraft derived values from particle probe data and airborne Sun photometer AATS-6 measurements were 0.88 and 0.83, respectively. Besides the uncertainties from the nonspherical effect of dust aerosols, sensitivity studies showed that the uncertainties (Δτ) of the GOES 8 retrieved AOT values were mainly from the uncertainties due to the imaginary part of refractive index (Δτ = ±0.05) and surface reflectance [Δτ = ±(0.02 ∼ 0.04)]. This paper demonstrates the application of geostationary satellites to detect and retrieve dust AOT even at low to moderate AOTs. The GOES 8 imager with high temporal resolutions also captures aerosol diurnal variation in this study that can further reduce the uncertainties in the current aerosol forcing estimations caused by the high temporal variations of AOT, thereby playing a complementary role with global AOT retrievals from polar orbiting satellites.
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GOES 8 and noaa 14 avhrr retrieval of smoke aerosol optical thickness during scar b
International Journal of Remote Sensing, 2002Co-Authors: Sundar A Christopher, B N Holben, Jianglong Zhang, S K YangAbstract:Using the NOAA-14 1-km Advanced Very High Resolution Radiometer (AVHRR) and the Geostationary Operational Environmental Satellite (GOES-8) imager data, smoke aerosol optical thickness ( ) is retrieved over land during the Smoke, Clouds and Radiation-Brazil (SCAR-B) experiment in Brazil during August-September 1995. The satellite-retrieved values are then compared against ground-based sunphotometer derived values from the Aerosol Robotic Network (AERONET) program. Both the AVHRR and GOES-8 retrieved values are in excellent agreement with the AERONET derived values with linear correlation coefficients of 0.93. A single scattering albedo of 0.90 (at 0.67 w m) provides the best fit between the GOES-8 and AERONET values. The sensitivity of the retrieved to assumed surface albedo and aerosol single scattering albedo are also examined. A simple multi-spectral thresholding algorithm is used to separate smoke from other features from GOES-8 satellite imagery and regional maps of are provided. Our r...
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intercomparison of smoke aerosol optical thickness derived from GOES 8 imager and ground based sun photometers
Journal of Geophysical Research, 2001Co-Authors: Jianglong Zhang, Sundar A Christopher, B N HolbenAbstract:Using high temporal resolution GOES 8 imager data and radiative transfer calculations, smoke aerosol optical thickness (τ) is retrieved over selected sites in South America and Central America. The degradation of the signal response in the GOES 8 visible channel is estimated and the satellite-retrieved τ values are then compared against ground-based Sun photometer derived values. The satellite-retrieved values are in good agreement with ground-based τ for two sites in South America with mean linear correlation coefficients of 0.97. For Central America the mean correlation coefficient is 0.80. A single scattering albedo of 0.90 (at 0.67 μm) yields the best agreement between ground-based and satellite retrieved values and is consistent with previous studies. However, our results show that the retrieved optical thickness results are sensitive to single scattering albedo and surface reflectance. For example, a ±3.3% change in single scattering albedo (0.90±0.03) yields an uncertainty in τ of 10% for small optical thickness (τ = 0.5) and an uncertainty of about 25% for larger optical thickness values (τ = 1.5). Although the GOES 8 visible channel has undergone significant degradation in signal response since launch, smoke aerosol optical thickness can be estimated if proper procedures are used to account for this effect.
Patrick Minnis - One of the best experts on this subject based on the ideXlab platform.
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comparison of cirrus optical depths derived from GOES 8 and surface measurements
Journal of Geophysical Research, 2004Co-Authors: Qilong Min, Patrick Minnis, Mandana M KhaiyerAbstract:[1] Ground-based passive radiometer measurements are used to validate satellite-derived cirrus optical depths over the Atmospheric Radiation Measurement Program Southern Great Plains site during March 2000. Optical depths derived from direct beam measurements by a multifilter rotating shadow band radiometer were well correlated with those determined from the Geostationary Operational Environmental Satellite, especially in relatively homogenous cloud fields. Compared to the multifilter rotating shadow band radiometer (MFRSR) results, on average, the satellite retrieval overestimated optical depth by ∼0.67 (29%), even though 75% of the GOES values were within ±1.0 of the MFRSR results. Some of the bias is attributable to cloud inhomogeneities, mismatches in observed clouds, errors in the surface albedo, and possible errors in the ice crystal scattering phase function. The results demonstrate the potential for using MFRSR data, available over many parts of the globe, for validating satellite cloud retrievals in many different surface and atmospheric conditions.
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validation of satellite derived liquid water paths using arm sgp microwave radiometers
2003Co-Authors: Mandana M Khaiyer, William L Smith, Patrick Minnis, J Huang, Bing Lin, Anita D RappAbstract:Satellites are useful for monitoring climatological parameters over large domains. They are especially useful for measuring various cloud microphysical and radiative parameters where ground-based instruments are not available. The geostationary operational environmental satellite (GOES) has been used to retrieve cloud and radiative properties over an extended domain centered on the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (CF). One of the microphysical parameters available from the GOES-8 dataset is cloud liquid water path (LWP), which is crucial for linking the atmospheric hydrological and radiative budgets. Preliminary validation of this parameter has been limited to a very few cases of thick stratus during March 2000. To better understand and validate the GOES-derived LWP more completely, this paper compares it with LWP retrievals based on ARM’s ground-based microwave radiometers (MWR) at the SGP central and boundary facilities. The comparisons utilize data taken in a variety of cloud conditions during March 2000 to examine the relationships between the GOES-8 and microwave LWP retrievals as related to cloud temperature, cloud type, and viewing angle.
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rapid calibration of operational and research meteorological satellite imagers part i evaluation of research satellite visible channels as references
Journal of Atmospheric and Oceanic Technology, 2002Co-Authors: Patrick Minnis, Louis Nguyen, David R Doelling, David F Young, Walter F Miller, David P KratzAbstract:Operational meteorological satellites generally lack reliable onboard calibration systems for solar-imaging channels. Current methods for calibrating these channels and for normalizing similar channels on contemporaneous satellite imagers typically rely on a poorly calibrated reference source. To establish a more reliable reference instrument for calibration normalization, this paper examines the use of research satellite imagers that maintain their solar-channel calibrations by using onboard diffuser systems that rely on the sun as an absolute reference. The Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission(TRMM) satellite and the second Along-Track Scanning Radiometer (ATSR-2) on the second European Remote Sensing Satellite (ERS-2) are correlated with matched data from the eighth Geostationary Operational Environmental Satellite (GOES-8), the fifth Geostationary Meteorological satellite(GMS-5), and with each other to examine trends in the solar channels. VIRS data are also correlated with the Terra satellite’s Moderate Resolution Imaging Spectroradiometer (MODIS) provisional data as a preliminary assessment of their relative calibrations. As an additional check on their long-term stability, the VIRS data are compared to the relevant corresponding broadband shortwave radiances of the Clouds and the Earth’s Radiant Energy System (CERES) scanners on TRMM. No statistically significant trend in the calibration of the VIRS 0.65- and 1.64-mm channels could be detected from the comparisons with CERES data taken during 1998 and 2000. The VIRS-to-GOES-8 correlations revealed an annual degradation rate for the GOES-8 visible (0.67 mm) channel of ;7.5% and an initial drop of 16% in the gain from the prelaunch value. The slopes in the GOES-8 visible-channel gain trend lines derived from VIRS data taken after January 1998 and ATSR-2 data taken between October 1995 and December 1999 differed by only 1%‐2% indicating that both reference instruments are highly stable. The mean difference of 3%‐4.8% between the VIRS‐GOES-8 and ATSR-2‐GOES-8 gains is attributed to spectral differences between ATSR-2 and VIRS and to possible biases in the ATSR-2 channel-2 calibration. A degradation rate of 1.3% per year found for the GMS-5 visible channel was confirmed by comparisons with earlier calibrations. The MODIS and VIRS calibrations agreed to within 21% to 3%. Some of the differences between VIRS and the provisional MODIS radiances can be explained by spectral differences between the two instruments. The MODIS measures greater reflectance than VIRS for bright scenes. Although both VIRS and ATSR-2 provide temporally stable calibrations, it is recommended that, at least until MODIS calibrations are finalized, VIRS should be used as a reference source for normalizing operational meteorological satellite imagers because of its broader visible filter.
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rapid calibration of operational and research meteorological satellite imagers part ii comparison of infrared channels
Journal of Atmospheric and Oceanic Technology, 2002Co-Authors: Patrick Minnis, Louis Nguyen, David R Doelling, David F Young, Walter F Miller, David P KratzAbstract:To establish a more reliable reference instrument for calibration normalization, this paper examines the differences between the various thermal infrared imager channels on a set of research and operational satellites. Mean brightness temperatures from the Visible Infrared Scanner (VIRS) on the Tropical Rainfall Measuring Mission (TRMM) satellite and the second Along-Track Scanning Radiometer (ATSR-2) on the second European Remote Sensing Satellite (ERS-2) are correlated with matched data from the eighth Geostationary Operational Environmental Satellite (GOES-8), the fifth Geostationary Meteorological Satellite (GMS-5), and with each other. VIRS data are also correlated with the Terra satellite’s Moderate Resolution Imaging Spectroradiometer (MODIS) provisional data as a preliminary assessment of their relative calibrations. As an additional check on their long-term stability, the VIRS data are compared to the broadband longwave radiances of the Clouds and the Earth’s Radiant Energy System (CERES) scanners on TRMM. No statistically significant trend in the calibration of any of the three (3.7, 10.8, and 12.0 mm) VIRS thermal channels could be detected from the comparisons with CERES data taken during 1998 and 2000 indicating that the VIRS channels can serve as a reliable reference for intercalibrating satellite imagers. However, a small day‐night difference in the VIRS thermal channels detected at very low temperatures should be taken into account. In general, most of the channels agreed to within less than 60.7 K over a temperature range between 200 and 300 K. Some of the smaller differences can be explained by spectral differences in the channel response functions. A few larger differences were found at 200 K for some of the channels suggesting some basic calibration differences for lower temperatures. A nearly 3-K bias in the ATSR-2 11-mm channel relative to VIRS and GOES-8 was found at the cold end of the temperature range. The intercalibrations described here are being continued on a routine basis.
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comparison of scarab GOES 8 aircraft and surface observations of the absorption of solar radiation by clouds
Journal of Geophysical Research, 2002Co-Authors: Shelly K Pope, Francisco P J Valero, William D Collins, Patrick MinnisAbstract:Data obtained by the Scanner for Radiation Budget (ScaRaB) instrument on the Meteor 3 satellite have been analyzed and compared to satellite (GOES 8), aircraft (Radiation Measurement System, RAMS), and surface (Baseline Solar Radiation Network (BSRN), Solar and Infrared Observations System (SIROS), and RAMS) measurements of irradiance obtained during the Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE). It is found that the ScaRaB data covering the period from March 1994 to February 1995 (the instrument's operational lifetime) indicate excess absorption of solar radiation by the cloudy atmosphere in agreement with previous aircraft, surface, and GOES 8 results. The full ScaRaB data set combined with BSRN and SIROS surface observations gives an average all-sky absorptance of 0.28. The GOES 8 data set combined with RAMS surface observations gives an average all-sky absorptance of 0.26. The aircraft data set (RAMS) gives a mean all-sky absorptance of 0.24 (for the column between 0.5 and 13 km).