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Lee S.-W.,Pusan National University | Kouba J.,Natural Resources Canada | Schutz B.,University of Texas at Austin | Kim D.H.,National Meteorological Satellite Center | Lee Y.J.,Konkuk University
Journal of Geodesy | Year: 2013

This paper addresses real-time monitoring of the precipitable water vapor (PWV) from GNSS measurements and presents some results obtained from 6-month long GNSS PWV experiments using international and domestic GNSS networks. In the real-time GNSS PWV monitoring system a server/client structure is employed to facilitate formation of PWV networks and single-differenced GNSS measurements are utilized to mitigate errors in GNSS satellites' orbits and clocks. An issue relating to baseline length between the server and clients is discussed in detail and as a result the PWV monitor is configured to perform in two modes depending on the baseline length. The server estimates sequentially the zenith wet delay of the individual stations, which is then converted into the PWV of the stations. We evaluate system performance by comparing the real-time PWV solution with reference solutions including meteorological measurements obtained with radiosondes and deferred-time precision GNSS PWV solutions. Results showed that the standard deviation of difference between the real-time PWV and the reference solutions ranged from 2.1 to 3.4 mm in PWV for a 6-month long comparison, which was improved to 1.4 to 2.9 mm by reducing comparison period to 20 days in winter. © 2013 Springer-Verlag Berlin Heidelberg.

Jin Y.-Q.,Fudan University | Lu N.,National Meteorological Satellite Center | Lin M.,State Oceanic Administration
Proceedings of the IEEE | Year: 2010

During recent decades, China has successfully launched several programs of satellite-borne remote sensing, including the meteorological Feng-Yun (FY, wind cloud) series and oceanic Hai-Yang (HY, ocean) series, in broad spectra, i.e., optical, infrared, and microwave. Since the initiation from the early 1970s, a total of nine meteorological satellites, FY series, including five polar-orbit satellites and four geostationary satellites, have been successfully launched. Chinese FY has become an important component of global meteorological satellites systems and continues to maintain long-term stable operations of both polar and stationary meteorological satellites. Later in 2002, China's HY-1, an oceanic color satellite, was launched and is now in good operation. The successive HY-2 and HY-3 of the HY series, including microwave sensors, are also on schedule. Relevant basic research, application, and operational service of satellite-borne remote sensing and Earth observation have been well implemented. In this paper, a brief overview of Chinese satellite-borne remote sensing, FY and HY series, is presented, and some progress is introduced. © 2006 IEEE.

Zhang Y.,National Meteorological Satellite Center | Gunshor M.M.,University of Wisconsin - Madison
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

The Fengyun (FY)-2 series satellites are the first-generation geosynchronous (GEO) Earth observation satellites operated by the National Satellite Meteorological Center (NSMC), China Meteorological Administration (CMA). The FY-2 satellites' main payload is a multispectral imager. The radiances from the FY-2C/D/E imagers were compared to the Atmospheric Infrared Sounder (AIRS), which is in low Earth orbit (LEO) on Aqua, a National Aeronautics and Space Administration satellite. The intercalibration of FY-2C/D/E infrared (IR) channels using AIRS was carried out based on the Global Space-based Inter-Calibration System (GSICS) GEO-LEO intercalibration algorithm. All the FY-2C/D/E data archived at the Cooperative Institute for Meteorological Satellite Studies, Space Science and Engineering Center, University of Wisconsin-Madison, Madison, WI, USA, were processed and compared with their operational calibrations. Select comparisons and longer term analyses between the new intercalibrated results and the operational calibrations of FY-2C/D/E's IR channels were demonstrated. The results show that the current operational calibration for FY-2C/D/E does not compare favorably based on the FY-AIRS intercalibration. The future operational calibration of FY-2D and FY-2E could be revised using GSICS corrections from the intercalibration with AIRS. The historical FY-2C/D/E data could be recalibrated with the GSICS GEO-LEO intercalibration algorithm at NSMC/CMA. © 2012 IEEE.

Hong S.,National Meteorological Satellite Center
Remote Sensing of Environment | Year: 2010

Polar ice masses and sheets are sensitive indicators of climate change. Small-scale surface roughness significantly impacts the microwave emission of the sea ice/snow surface; however, published results of surface roughness measurements of sea ice are rare. Knowing the refractive index is important to discriminate between objects. In this study, the small-scale roughness and refractive index over sea ice are estimated with AMSR-E observations and a unique method. Consequently, the small-scale surface roughness of 0.25 cm to 0.5 cm at AMSR-E 6.9 GHz shows reasonable agreement with the results of known observations, ranging from 0.2 cm to 0.6 cm for the sea ice in the Antarctic and Arctic regions. The refractive indexes are retrieved from 1.6 to 1.8 for winter, from 1.2 to 1.4 for summer in the Arctic and the Antarctic, which are similar to those of the sea ice and results from previous studies. This research shows the physical characteristics of the sea ice edges and melting process. Accordingly, this investigation provides an effective procedure for retrieving the small-scale roughness and refractive index of sea ice and snow. Another advantage of this study is the ability to distinguish sea ice from the sea surface by their relative small-scale roughness. © 2009 Elsevier Inc. All rights reserved.

Kim D.,National Meteorological Satellite Center | Ramanathan V.,University of California at San Diego
Geophysical Research Letters | Year: 2012

This study integrates available surface-based and satellite observations of solar radiation at the surface and the top of the atmosphere (TOA) with a comprehensive set of satellite observations of atmospheric and surface optical properties and a Monte Carlo Aerosol-Cloud-Radiation (MACR) model to estimate the three fundamental components of the planetary solar radiation budget: Albedo at the TOA; atmospheric solar absorption; and surface solar absorption. The MACR incorporates most if not all of our current understanding of the theory of solar radiation physics including modern spectroscopic water vapor data, minor trace gases, absorbing aerosols including its effects inside cloud drops, 3-D cloud scattering effects. The model is subject to a severe test by comparing the simulated solar radiation budget with data from 34 globally distributed state-of-the art BSRN (Baseline Surface Radiation Network) land stations which began data collection in the mid 1990s. The TOA over these sites were obtained from the CERES (Cloud and Earth's Radiant Energy System) satellites. The simulated radiation budget was within 2 Wm-2 for all three components over the BSRN sites. On the other hand, over these same sites, the IPCC-2007 simulation of atmospheric absorption is smaller by 7-8 Wm-2. MACR was then used with a comprehensive set of model input from satellites to simulate global solar radiation budget. The simulated planetary albedo of 29.0% confirms the value (28.6%) observed by CERES. We estimate the atmospheric absorption to be 82 8 Wm-2 to be compared with the 67 Wm-2 by IPCC models as of 2001 and updated to 76 Wm-2 by IPCC-2007. The primary reasons for the 6 Wm-2 larger solar absorption in our estimates are: updated water vapor spectroscopic database (∼1 Wm-2), inclusion of minor gases (∼0.5 Wm-2), black and brown carbon aerosols (∼4 Wm-2), the inclusion of black carbon in clouds (∼1 Wm-2) and 3-D effect of clouds (∼1 Wm-2). The fundamental deduction from our study is the remarkable consistency between satellite measurements of the radiation budget and the parameters (aerosols, clouds and surface reflectivity) which determine the radiation budget. Because of this consistency we can account for and explain the global solar radiation budget of the planet within few Wm-2. © 2012. American Geophysical Union. All Rights Reserved.

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