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University Park, MD, United States

Wang W.,5830 University Research Ct | Cao C.,National Oceanic and Atmospheric Administration
Remote Sensing | Year: 2016

The Visible and Infrared Imaging Radiometer Suite (VIIRS) onboard the Joint Polar Satellite System (JPSS)/Suomi National Polar-Orbiting Partnership (SNPP) satellite provide sensor data records for the retrievals of many environment data records. It is critical to monitor the VIIRS long-term calibration stability to ensure quality EDR retrieval. This study investigates the radiometric calibration stability of the NOAA operational SNPP VIIRS Reflective Solar Bands (RSB) and Day-Night-Band (DNB) using Deep Convective Clouds (DCC). Monthly and semi-monthly DCC time series for 10 moderate resolution bands (M-bands, M1-M5 and M7-M11, March 2013-September 2015), DNB (March 2013-September 2015, low gain stage), and three imagery resolution bands (I-bands, I1-I3, January 2014-September 2015) were developed and analyzed for long-term radiometric calibration stability monitoring. Monthly DCC time series show that M5 and M7 are generally stable, with a stability of 0.4%. DNB has also been stable since May 2013, after its relative response function update, with a stability of 0.5%. The stabilities of M1-M4 are 0.6%-0.8%. Large fluctuations in M1-M4 DCC reflectance were observed since early 2014, correlated with F-factor (calibration coefficients) trend changes during the same period. The stabilities of M8-M11 are from 1.0% to 3.1%, comparable to the natural DCC variability at the shortwave infrared spectrum. DCC mean band ratio time series show that the calibration stabilities of I1-I3 follow closely with M5, M7, and M10. Relative calibration changes were observed in M1/M4 and M5/M7 DCC mean band ratio time series. The DCC time series are generally consistent with results from the VIIRS validation sites and VIIRS/MODIS (the Moderate-resolution Imaging Spectroradiometer) simultaneous nadir overpass time series. Semi-monthly DCC time series for RSB M-bands and DNB were compared with monthly DCC time series. The results indicate that semi-monthly DCC time series are useful for stability monitoring at higher temporal resolution. © 2015 by the authors; licensee MDPI, Basel, Switzerland. Source

Zhou X.,5830 University Research Ct | Wang B.,University of Hawaii at Manoa
Journal of Geophysical Research: Atmospheres | Year: 2013

Secondary eyewalls are frequently observed in intense tropical cyclones (TCs). The separation distance between the primary eyewall and the secondary eyewall can vary from 10 to more than 100 km. The size of the secondary eyewall is a key factor determining the horizontal scale of the destructive winds and heavy rainfall in these TCs. Previous work suggested that the internal dynamic and thermodynamic structure of the TC affects the radial location of secondary eyewall formation. The potential impact of the large-scale environment is examined by using the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis and best track data sets in this study. It is found that large secondary eyewalls tend to form in weak storms at relatively high latitudes and in environments with high relative humidity, low sea-level pressure, and high low-level vorticity. The performance of a statistical-dynamical model to predict the size of secondary eyewalls is evaluated, and the physical interpretation of the selected predictors is also provided. Key Points Secondary eyewall size is related to storm intensity Environment affects secondary eyewall size A statistical model is evaluated ©2013. American Geophysical Union. All Rights Reserved. Source

Madhavan S.,Science Systems And Applications Inc. | Sun J.,5830 University Research Ct | Xiong X.,NASA | Wenny B.N.,Sigma Space Corporation | Wu A.,Sigma Space Corporation
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The first MODerate-resolution Imaging Spectroradiometer (MODIS), also known as the Proto-Flight model (PFM), is on-board the Terra spacecraft and has completed 14 years of on orbit flight as of December 18, 2013. MODIS remotely senses the Earth in 36 spectral bands, with a wavelength range from 0.4 μm to 14.4 μm. The 36 bands can be subdivided into two groups based on their spectral responsivity as Reflective Solar Bands (RSBs) and Thermal Emissive Bands (TEBs). Band 27 centered at 6.77 μm is a TEB used to study the global water vapor distribution. It was found recently that this band has been severely affected by electronic crosstalk. The electronic crosstalk magnitude, its on-orbit change and calibration impact have been well characterized in our previous studies through the use of regularly scheduled lunar observations. Further, the crosstalk correction was implemented in Earth view (EV) images and quantified the improvements of the same. However, improvements remained desirable on several fronts. Firstly, the effectiveness of the correction needed to be analyzed spatially and radiometrically over a number of scenes. Also, the temporal aspect of the correction had to be investigated in a rigorous manner. In order to address these issues, a one-orbit analysis was performed on the Level 1A (L1A) scene granules over a ten year period from 2003 through 2012. Results have been quantified statistically and show a significant reduction of image striping, as well as removal of leaked signal features from the neighboring bands. Statistical analysis was performed by analyzing histograms of the one-orbit granules at a scene and detector level before and after correction. The comprehensive analysis and results reported in this paper will be very helpful to the scientific community in understanding the impacts of crosstalk correction on various scenes and could potentially be applied for future improvements of band 27 calibration and, therefore, its retrieval for the Level 2 (L2) geophysical parameters. © 2014 SPIE. Source

Chen M.,5830 University Research Ct | Weng F.,College Park
Journal of Geophysical Research: Atmospheres | Year: 2012

Recent modeling results have indicated that, in general, idealized homogeneous spheroidal models of ice crystals and snowflakes cannot consistently describe radar backscattering from snowfall when the radar wavelengths are on the order of the snowflake size. In this paper, we provide empirical evidence supporting this prediction by analyzing collocated airborne radar measurements at 13.4 GHz, 35.6 GHz and 94 GHz. The analysis is performed by applying a recently developed method making use of two simultaneously measured dual-frequency ratios, allowing one to distinguish between the multifrequency backscattering behavior of detailed aggregate snow models and that of homogeneous spheroids. We demonstrate that in some naturally occurring cases, detailed snowflake models, which account for their complex structure, are required to describe backscattering by these particles in a manner that is consistent over multiple wavelengths. This implies that the spheroidal approximation is not always adequate as a snowflake s ape model in radar retrievals at this wavelength range. © 2012. American Geophysical Union. All Rights Reserved. Source

Mo K.C.,5830 University Research Ct | Shukla S.,University of Washington | Shukla S.,University of California at Santa Barbara | Lettenmaier D.P.,University of Washington | Chen L.-C.,The Interdisciplinary Center
Geophysical Research Letters | Year: 2012

We investigated whether seasonal soil moisture forecasts derived from a land surface model forced by seasonal climate forecast model outputs are more skillful than benchmark forecasts derived from the same land surface model but with forcings taken from resampled climatological precipitation, temperature and low level winds. For most forecast leads and over the western United States, soil moisture forecasts based on seasonal climate forecasts are no more skillful than the benchmark. For relatively short (one month) leads, the climate model-based forecasts are more skillful than the benchmark along a swath from the Gulf States to the Tennessee and Ohio Valleys and the Southwest monsoon region, where the climate model has skillful precipitation forecasts. © 2012. American Geophysical Union. All Rights Reserved. Source

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