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Yoo J.-M.,Ewha Womans University | Jeong M.-J.,Goddard Earth Science and Technology Center | Jeong M.-J.,NASA | Hur Y.M.,Ewha Womans University | Shin D.-B.,Yonsei University
Asia-Pacific Journal of Atmospheric Sciences | Year: 2010

This study analyzes radiative effect of the higher clouds over the fog layer and presents the improvement of fog detection over the Korean peninsula, utilizing satellite data of the Multi-functional Transport SATellite (MTSAT)-IR and the MODerate resolution Imaging Spectroradiometer (MODIS) and the Look-Up Table (LUT) based on Radiative Transfer Model (RTM) simulations. Fog detection utilizing the satellite data from visible (0.68 μm) and infrared (3.75 μm and 10.8 μm) channels has been evaluated in comparison with groundbased observations over 52 meteorological stations in the Korean Peninsula from March 2006 to February 2007. The threshold values for fog sensing have been derived from the difference (i.e., T3.7-11) in brightness temperature between 3.75 μm (T3.7) and 10.8 μm (T11) during day and night, and also from the reflectivity at 0.68 μm (R0.68) in the daytime. In the twilight, however, the difference between the temperature values at 10.8 μm and their maximum within previous 15 days (i.e., T IImax-II) are used instead, because the 3.75 μm channel is inaccurate for the fog detection at dawn/dusk. The sensitivity of the T 3.7-11 values with respect to the clouds is investigated based on the cloud variables such as its height, optical thickness, and amount. The values of T3.7-11 are the most sensitive to cloud height, followed by cloud optical thickness and effective radius, while R0.68 is insensitive to cloud height. The sensitivity is examined with various conditions of cloud phases and day/night. Sixteen cases among eighteen fog occurrences, which have been unable to be sensed by using only the conventional threshold values, are successfully detected with the additional LUT corrections, indicating a significant improvement. The method of fog detection in this study can be useful to the Communication, Ocean, and Meteorological Satellite (COMS) Meteorological Data Processing System (CMDPS) by reducing the cloud effect on fog sensing. © The Korean Meteorological Society and Springer 2010. Source

Georgieva E.M.,Goddard Earth Science and Technology Center | Heaps W.S.,NASA | Huang W.,Science Systems And Applications Inc.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2010

Accurate global measurement of carbon dioxide column with the aim of discovering and quantifying unknown sources and sinks has been a high priority for the last decade. In order to uncover the "missing sink" that is responsible for the large discrepancies in the budget the critical precision for a measurement from space needs to be on the order of 1ppm [1]. To better understand the CO 2 budget and to evaluate its impact on global warming the National Research Council (NRC) in its recent decadal survey report (NACP) to NASA recommended a laser based total CO 2 mapping mission in the near future [2]. That's the goal of Active Sensing of CO 2 Emissions over Nights, Days, and Seasons (ASCENDS) mission-to significantly enhance the understanding of the role of CO 2 in the global carbon cycle. Our current goal is to develop an ultra precise, inexpensive new lidar system for column measurements of CO 2 changes in the lower atmosphere that uses a Fabry-Perot interferometer based system as the detector portion of the instrument and replaces the narrow band laser commonly used in lidars with a high power broadband source. This approach reduces the number of individual lasers used in the system and considerably reduces the risk of failure. It also tremendously reduces the requirement for wavelength stability in the source putting this responsibility instead on the Fabry-Perot subsystem. © 2010 IEEE. Source

Levy R.C.,Science Systems And Applications Inc. | Levy R.C.,NASA | Remer L.A.,NASA | Kleidman R.G.,Science Systems And Applications Inc. | And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2010

NASA's MODIS sensors have been observing the Earth from polar orbit, from Terra since early 2000 and from Aqua since mid 2002. We have applied a consistent retrieval and processing algorithm to both sensors to derive the Collection 5 (C005) dark-target aerosol products over land. Here, we validate the MODIS along-orbit Level 2 products by comparing to quality assured Level 2 AERONET sunphotometer measurements at over 300 sites. From 85 463 collocations, representing mutually cloud-free conditions, we find that >66% (one standard deviation) of MODIS-retrieved aerosol optical depth (AOD) values compare to AERONETobserved values within an expected error (EE) envelope of ±(0.05 + 15%), with high correlation (R = 0.9). Thus, the MODIS AOD product is validated and quantitative. However, even though we can define EEs for MODIS-reported Ångström exponent and fine AOD over land, these products do not have similar physical validity. Although validated globally, MODIS-retrieved AOD does not fall within the EE envelope everywhere. We characterize some of the residual biases that are related to specific aerosol conditions, observation geometry, and/or surface properties, and relate them to situations where particular MODIS algorithm assumptions are violated. Both Terra's and Aqua's-retrieved AOD are similarly comparable to AERONET, however, Terra's global AOD bias changes with time, overestimating (by∼0.005) before 2004, and underestimating by similar magnitude after. This suggests how small calibration uncertainties of <2% can lead to spurious conclusions about long-term aerosol trends. © 2010 Author(s). Source

Patadia F.,Goddard Earth Science and Technology Center | Christopher S.A.,University of Alabama in Huntsville
Remote Sensing of Environment | Year: 2014

The Clouds and the Earth's Radiant Energy System (CERES) data has been used by several studies to calculate the top of atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) of biomass burning aerosols over land. However, the current CERES angular distribution models that are used to convert measured TOA radiances to fluxes are not characterized by aerosols. Using our newly developed empirical angular models for smoke aerosols we calculate the SWARF over South America for eight years (2000-2008) during the biomass burning season. Our results indicate that when compared to our new angular distribution model-derived values, the instantaneous SWARF is underestimated by the CERES data by nearly 3.3Wm-2. Our studies indicate that it is feasible to develop angular models using empirical methods that can then be used to reduce uncertainties in aerosol radiative forcing calculations. More importantly, empirically-based methods for calculating radiative forcing can serve as a benchmark for modeling studies. © 2013 Elsevier Inc. Source

Utku C.,Goddard Earth Science and Technology Center | Lang R.H.,George Washington University
2011 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011 | Year: 2011

Due to their highly random nature, vegetation canopies can be modeled using the incoherent transport theory for active and passive remote sensing applications. Agricultural vegetation canopies however are generally more structured than natural vegetation. The inherent row structure in agricultural canopies induces coherence effects disregarded by the transport theory. The objective of this study is to demonstrate, via Monte-Carlo simulations, these coherence effects on L-band scattering and thermal emission from corn canopies consisting of only stalks. © 2011 IEEE. Source

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