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Cheng J.,Beijing Normal University | Liang S.,Beijing Normal University | Liang S.,University of Maryland University College | Wang W.,Earth Resource Technology Inc. | Guo Y.,Beijing Normal University
Journal of Geophysical Research: Atmospheres | Year: 2017

This paper proposes an efficient hybrid method for estimating 1 km instantaneous clear-sky surface downward longwave radiation (LWDN) from Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared observations and the MODIS near-infrared column water vapor (CWV) data product. The LWDN was formulated as a nonlinear function of surface upwelling longwave radiation estimated from the MODIS top-of-atmosphere (TOA) radiance of channels 29, 31, and 32, as well as CWV and the MODIS TOA radiance of channel 29. Ground measurements collected at 62 globally distributed sites from six networks were used to develop and validate the proposed hybrid method. The validation results showed that the bias and root-mean-square error (RMSE) were 0.0597 W/m2 and 21.008 W/m2. These results demonstrate that the performance of our method is superior to that of other studies reported in the literature. The drawback of our method is that LWDN is overestimated over high-elevation areas with extremely low CWV (<0.5 g/cm2) and underestimated over regions with tropical climates that have extremely high CWV. A power function relating LWDN to CWV was derived and used as a complementary method to address these circumstances. The overestimation was overcome, and the bias and RMSE decreased from 9.407 W/m2 and 23.919 W/m2 to −0.924 W/m2 and 19.895 W/m2. The underestimation was also alleviated. ©2017. American Geophysical Union. All Rights Reserved.


Randel W.J.,U.S. National Center for Atmospheric Research | Smith A.K.,U.S. National Center for Atmospheric Research | Wu F.,U.S. National Center for Atmospheric Research | Zou C.-Z.,The Center for Satellite Applications and Research | Qian H.,Earth Resource Technology Inc.
Journal of Climate | Year: 2016

Temperature trends in the middle and upper stratosphere are evaluated using measurements from the Stratospheric Sounding Unit (SSU), combined with data from the Aura Microwave Limb Sounder (MLS) and Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) instruments. Data from MLS and SABER are vertically integrated to approximate the SSU weighting functions and combined with SSU to provide a data record spanning 1979-2015. Vertical integrals are calculated using empirically derived Gaussian weighting functions, which provide improved agreement with high-latitude SSU measurements compared to previously derived weighting functions. These merged SSU data are used to evaluate decadal-scale trends, solar cycle variations, and volcanic effects from the lower to the upper stratosphere. Episodic warming is observed following the volcanic eruptions of El Chichón (1982) and Mt. Pinatubo (1991), focused in the tropics in the lower stratosphere and in high latitudes in the middle and upper stratosphere. Solar cycle variations are centered in the tropics, increasing in amplitude from the lower to the upper stratosphere. Linear trends over 1979-2015 show that cooling increases with altitude from the lower stratosphere (from ~-0.1 to -0.2 K decade-1) to the middle and upper stratosphere (from ~-0.5 to -0.6 K decade-1). Cooling in the middle and upper stratosphere is relatively uniform in latitudes north of about 30°S, but trends decrease to near zero over the Antarctic. Mid- and upper-stratospheric temperatures show larger cooling over the first half of the data record (1979-97) compared to the second half (1998-2015), reflecting differences in upper-stratospheric ozone trends between these periods. © 2016 American Meteorological Society.


Wang W.,Earth Resource Technology Inc. | Zou C.-Z.,The Center for Satellite Applications and Research
Journal of Atmospheric and Oceanic Technology | Year: 2014

The Advanced Microwave Sounding Unit-A (AMSU-A, 1998-present) not only continues but surpasses the Microwave Sounding Unit's (MSU, 1978-2006) capability in atmospheric temperature observation. It provides valuable satellite measurements for higher vertical resolution and long-term climate change research and trend monitoring. This study presented methodologies for generating 11 channels of AMSU-A-only atmospheric temperature data records from the lower troposphere to the top of the stratosphere. The recalibrated AMSU-A level 1c radiances recently developed by the Center for Satellite Applications and Research group were used. The recalibrated radiances were adjusted to a consistent sensor incidence angle (nadir), channel frequencies (prelaunch-specified central frequencies), and observation time (local solar noon time). Radiative transfer simulations were used to correct the sensor incidence angle effect and the National Oceanic and Atmospheric Administration-15 (NOAA-15) channel 6 frequency shift.Multiyear averaged diurnal/ semidiurnal anomaly climatologies from climate reanalysis as well as climate model simulations were used to adjust satellite observations to local solar noon time. Adjusted AMSU-A measurements from six satellites were carefully quality controlled and merged to generate 131 years (1998-2011) of a monthly 2.5° × 2.5° gridded atmospheric temperature data record.Major trend features in the AMSU-A-only atmospheric temperature time series, including global mean temperature trends and spatial trend patterns, were summarized. © 2014 American Meteorological Society.


Zou C.-Z.,The Center for Satellite Applications and Research | Qian H.,Earth Resource Technology Inc.
Journal of Atmospheric and Oceanic Technology | Year: 2016

Observations from the Stratospheric Sounding Unit (SSU) on board historical NOAA polar-orbiting satellites have played a vital role in investigations of long-term trends and variability in the middle- and upper-stratospheric temperatures during 1979-2006. The successor to SSU is the Advanced Microwave Sounding Unit-A (AMSU-A) starting from 1998 until the present. Unfortunately, the two observations came from different sets of atmospheric layers, and the SSU weighting functions varied with time and location, posing a challenge to merge them with sufficient accuracy for development of an extended SSU climate data record. This study proposes a variational approach for the merging problem, matching in both temperatures and weighting functions. The approach yields zero means with a small standard deviation and a negligible drift over time in the temperature differences between SSU and its extension to AMSU-A. These features made the approach appealing for reliable detection of long-term climate trends. The approach also matches weighting functions with high accuracy for SSU channels 1 and 2 and reasonable accuracy for channel 3. The total decreases in global mean temperatures found from the merged dataset were from 1.8 K in the middle stratosphere to 2.4 K in the upper stratosphere during 1979-2015. These temperature drops were associated with two segments of piecewise linear cooling trends, with those during the first period (1979-97) being much larger than those of the second period (1998-2015). These differences in temperature trends corresponded well to changes of the atmospheric ozone amount from depletion to recovery during the respective time periods, showing the influence of human decisions on climate change. © 2016 American Meteorological Society.


Wang W.,Earth Resource Technology Inc. | Cao C.,The Center for Satellite Applications and Research
Journal of Atmospheric and Oceanic Technology | Year: 2015

The Visible and Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-Orbiting Partnership satellite brings new opportunities for improving scientists' understanding of deep convective cloud (DCC) radiometry with multiple bands in the visible (VIS), near-infrared (NIR), and longwave infrared (LWIR) spectrum.This paper investigated the radiometric sensitivity of DCC reflectance to spatial resolution, brightness temperature of the LWIR band centered at ~11 μm (TB11), TB11 calibration bias, and cluster size using VIIRS VIS (M5), NIR (M7 and I2), and LWIR (M15 and I5) observations at 375-and 750-m spatial resolutions.The mean and mode of the monthly probability distribution functions of DCC reflectance are used as two important indices in using DCC for calibration, and the results show that the onboard radiometric calibration of M5, M7, and I2 are stable during May 2013-April 2014 despite severe instrument responsivity degradations.The standard deviations of the mean and mode of monthly DCC reflectance are 0.5% and 0.2%, respectively, for all bands.It was found that a TB11 calibration bias on the order of 0.5K has minimal impact on monthly DCC reflectance, especially when the mode method is used.The mean and mode of VIS and NIR DCC reflectance are functions of spatial resolution, TB11 threshold, and DCC cluster size in all seasons.However, the mode of DCC reflectance is more stable than the mean in terms of all three factors.Therefore, the mode is more suitable as an indicator of calibration stability for individual VIS and NIR bands. © 2015 American Meteorological Society.


Choi T.,Earth Resource Technology Inc. | Cao C.,The Center for Satellite Applications and Research | Weng F.,The Center for Satellite Applications and Research
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The Soumi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) was launched on October 28th, 2011 and its Sensor Data Record (SDR) product reached maturity status in March of 2014. Although the VIIRS SDR products are declared at the validated maturity level, there remain issues such as residual stripings in some thermal bands along with the scan direction. These horizontal striping issues in the Thermal Emissive Bands (TEB) were reflected in the sea surface temperature (SST) products. The observed striping magnitude can reach to 0.2 K, especially at the band M14 and M15. As an independent source of calibration, the Solar Diffuser (SD) is utilized in this study. The SD is originally designed for the Reflective Solar Band (RSB), however, it is assumed to be thermally stable at the time of SD observation. For each detector, a linear slope is developed by Integrated Calibration and Validation System (ICVS), which is applied on converting digital number (DN) to radiance unit. After the conversion, detector based noise analyses in VIIRS band M15 and M16 are performed on in-scan and scan-by-scan SD responses. Since SD radiance varies within an orbit, the noise calculation must be derived from the neighborhood Allan deviation. The noise derived Allan deviation shows that detector 1 and 2 in band M15 and detector 9 in band M16 have higher noise content compared to other detectors. © 2015 SPIE.


Wang W.,Earth Resource Technology Inc. | Cao C.,National Oceanic and Atmospheric Administration
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Post-launch monitoring of radiometric accuracy and stability of VIIRS (Visible Infrared Imaging Radiometer Suite) Solar Reflective Bands (RSB) at high gain stage (HGS) is essential for ocean color applications. This study investigates the absolute radiometric calibration accuracy of VIIRS bands M1-M5 at HGS using selected clear-sky dark ocean surfaces where top of atmosphere (TOA) signal is dominated by Rayleigh scattering. Vicarious gains were estimated using ratios between satellite observed and radiative transfer model simulated TOA reflectance. VIIRS TOA reflectance was simulated using 6SV (Second Simulation of a Satellite Signal in the Solar Spectrum - Vector, version 1.1). Input parameters required by the 6SV, including atmospheric profiles, wind speed and direction, aerosol optical thickness, and chlorophyll-A concentration, were obtained from the NASA Modern-Era Retrospective Analysis for Research and Applications reanalysis products, VIIRS aerosol optical thickness product, and previous studies. The Rayleigh scattering method developed in this study was applied to June to August 2014 VIIRS observations over six oceanic sites. Preliminary results indicated that the 3-month averaged vicarious gain for bands M1, M2, and M5 are close to 1. Relatively larger vicarious gains were observed in the other two bands, especially in band M4. The Rayleigh scattering calibration results generally agree with results from the VIIRS deep convective clouds time series analysis. © 2014 SPIE.


Imhoff M.L.,NASA | Zhang P.,NASA | Zhang P.,Earth Resource Technology Inc. | Wolfe R.E.,NASA | Bounoua L.,NASA
Remote Sensing of Environment | Year: 2010

Impervious surface area (ISA) from the Landsat TM-based NLCD 2001 dataset and land surface temperature (LST) from MODIS averaged over three annual cycles (2003-2005) are used in a spatial analysis to assess the urban heat island (UHI) skin temperature amplitude and its relationship to development intensity, size, and ecological setting for 38 of the most populous cities in the continental United States. Development intensity zones based on %ISA are defined for each urban area emanating outward from the urban core to the non-urban rural areas nearby and used to stratify sampling for land surface temperatures and NDVI. Sampling is further constrained by biome and elevation to insure objective intercomparisons between zones and between cities in different biomes permitting the definition of hierarchically ordered zones that are consistent across urban areas in different ecological setting and across scales. We find that ecological context significantly influences the amplitude of summer daytime UHI (urban-rural temperature difference) the largest (8 °C average) observed for cities built in biomes dominated by temperate broadleaf and mixed forest. For all cities combined, ISA is the primary driver for increase in temperature explaining 70% of the total variance in LST. On a yearly average, urban areas are substantially warmer than the non-urban fringe by 2.9 °C, except for urban areas in biomes with arid and semiarid climates. The average amplitude of the UHI is remarkably asymmetric with a 4.3 °C temperature difference in summer and only 1.3 °C in winter. In desert environments, the LST's response to ISA presents an uncharacteristic "U-shaped" horizontal gradient decreasing from the urban core to the outskirts of the city and then increasing again in the suburban to the rural zones. UHI's calculated for these cities point to a possible heat sink effect. These observational results show that the urban heat island amplitude both increases with city size and is seasonally asymmetric for a large number of cities across most biomes. The implications are that for urban areas developed within forested ecosystems the summertime UHI can be quite high relative to the wintertime UHI suggesting that the residential energy consumption required for summer cooling is likely to increase with urban growth within those biomes.


Zhang P.,NASA | Zhang P.,Earth Resource Technology Inc. | Imhoff M.L.,NASA | Wolfe R.E.,NASA | Bounoua L.,NASA
Canadian Journal of Remote Sensing | Year: 2010

Impervious surface area (ISA) from the National Geophysical Data Center (NGDC) and land surface temperature (LST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) averaged over three annual cycles (2003-2005) are used in a spatial analysis to assess the urban heat island (UHI) signature on LST amplitude and its relationship with development intensity, size, and ecological setting for more than 3000 urban settlements globally. Development intensity zones based on fractional ISA are defined for each urban area emanating outward from the urban core to the nearby nonurban rural areas and used to stratify sampling for LST. Sampling is further constrained by biome type and elevation data to ensure objective intercomparisons between zones and between cities in different biomes. We find that the ecological context and settlement size significantly influence the amplitude of summer daytime UHI. Globally, an average of 3.8 °C UHI is found in cities built in biomes dominated by forests; 1.9 °C UHI in cities embedded in grass-shrubs biomes; and only a weak UHI or sometimes an urban heat sink (UHS) in cities in arid and semi-arid biomes. Overall, the amplitude of the UHI is negatively correlated (R 5-0.66) with the difference in vegetation density between urban and rural zones represented by the MODIS normalized difference vegetation index (NDVI). Globally averaged, the daytime UHI amplitude for all settlements is 2.6 °C in summer and 1.4 °C in winter. Globally, the average summer daytime UHI is 4.7 °C for settlements larger than 500 km2 compared with 2.5 °C for settlements smaller than 50 km2 and larger than 10 km 2. The stratification of cities by size indicates that the aggregated amount of ISA is the primary driver of UHI amplitude, with variations between ecological contexts and latitudinal zones. More than 60% of the total LST variance is explained by ISA for urban settlements within forests at mid to high latitudes. This percentage will increase to more than 80% when only settlements in the US are examined. © 2010 CASI.


Zhang P.,NASA | Zhang P.,Earth Resource Technology Inc. | Imhoff M.L.,NASA | Bounoua L.,NASA | Wolfe R.E.,NASA
Canadian Journal of Remote Sensing | Year: 2012

Impervious surface area (ISA) from the National Land Cover Database 2001 and land surface skin temperature from MODIS averaged over three annual cycles (2003-2005) are used in a spatial analysis to assess the surface urban heat island (UHI) signature and its relationship to settlement size and shape, development intensity distribution, and land cover composition for 42 urban settlements embedded in forest biomes in the northeastern United States. Development intensity zones, based on percent ISA, are defined for each urban area emanating outward from the urban core to nearby rural areas and are used to stratify land surface temperature. The stratification is further constrained by biome type and elevation to ensure objective intercomparisons between urban zones within an urban settlement and between settlements. Stratification based on ISA allows the definition of hierarchically ordered urban zones that are consistent across urban settlements and scales. For cities within the northeastern US temperate mixed forest biome, we found that settlement size, shape, and development intensity significantly influenced the amplitude of summer daytime UHI. Our study indicates that for cities of similar size, the ISA density distribution within the urban area and the shape of the urbanized area as measured by area to perimeter ratio are significant modulators of UHI magnitude. Our results indicate that remotely sensed satellite data provide a consistent characterization of the UHI magnitude as well as its major drivers across regional scales. © 2012 CASI.

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