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Sunda S.,Space Applications Center Ahmedabad India | Sridharan R.,Physical Research Laboratory Ahmedabad India | Khekale P.V.,Space Applications Center Ahmedabad India | Parikh K.S.,Space Applications Center Ahmedabad India | And 4 more authors.
Space Weather | Year: 2015

Satellite-Based Augmentation Systems (SBASes) are designed to provide additional accuracy and robustness to existing satellite-based radio navigation systems for all phases of a flight. However, similar to navigation systems such as GPS which has proven its worth for the investigation of the ionosphere, the SBASes do have certain advantages. In the present paper, we propose and demonstrate SBAS applicability to ionospheric and space weather research in a novel and cost-effective way. The recent commissioning of the Indian SBAS, named GPS Aided Geo Augmented Navigation (GAGAN), covering the equatorial and low-latitude regions centered around the Indian longitudes provides the motivation for this approach. Two case studies involving different ionospheric behavior over low-latitude regions vindicate the potential of SBAS over extended areas. ©2014. American Geophysical Union.

Jindal P.,Indian Institute of Remote Sensing | Shukla M.V.,Space Applications Center Ahmedabad India | Sharma S.K.,Physical Research Laboratory Ahmedabad India | Thapliyal P.K.,Space Applications Center Ahmedabad India
Quarterly Journal of the Royal Meteorological Society | Year: 2016

The present work proposes a novel method to derive vertical profiles of ozone from infrared measurements on board geostationary sounders. The methodology is based on Principal Component Analysis (PCA) and has been applied over a large geographical region from 45°S to 45°N. It has been found that the first two principal components (PCs) together explain 71% of the total variance of the ozone profiles and are statistically significant and quite stable. Therefore, an algorithm for the retrieval of the first two PCs has been proposed. The magnitude of the retrieval error using PCA is significantly smaller than the variance of the dataset in the atmospheric layer from 200.0 to 5.0 hPa, indicating that the skill of the new algorithm is very high. The new algorithm was applied to the sounder observations from GOES-13 (Geostationary Operational Environmental Satellite) and INSAT-3D (Indian National Satellite) for the validation study. The validation of GOES-13 retrieved profiles with the ozonesonde has shown that the algorithm is working better in the stratosphere than in the troposphere. Furthermore, the GOES-13 retrieved ozone was also compared with the SBUV/2 (Solar Backscatter Ultraviolet) ozone. Overall the %RMSD (percentage root-mean-square deviation) values were within 30%. However, the values were within 10% above 20 hPa for most of the cases. The comparison of INSAT-3D retrieved profiles with SBUV/2 and OMPS (Ozone Mapping and Profiler Suite) profiles have shown results almost similar to GOES-13. The ozone values retrieved by using the existing algorithms and the algorithm presented in this work have been compared. It is found that the ozone retrieval has improved significantly with the algorithm presented in this work. © 2016 Royal Meteorological Society.

Singh R.,Space Applications Center Ahmedabad India | Ojha S.P.,Space Applications Center Ahmedabad India | Kishtawal C.M.,Space Applications Center Ahmedabad India | Pal P.K.,Space Applications Center Ahmedabad India | Kiran Kumar A.S.,Space Applications Center Ahmedabad India
Quarterly Journal of the Royal Meteorological Society | Year: 2015

The present study concentrates on the assimilation of clear-sky radiances from the recently launched INSAT-3D satellite. The imager and sounder are two primary meteorological instruments aboard the INSAT-3D satellite. Pre-assimilation monitoring of the radiances has been carried out from April to July 2014. A double-difference technique using the High Resolution Infrared Sounder (HIRS) on MetOp-A is employed to remove the effect of deficiencies in the model-analysed profiles which can contribute to the biases. Observed radiances of both instruments appear to be colder (∼1.5-2 K) with respect to radiative transfer model (RTM) simulated radiances, except water vapour channel radiances, which are warmer (0.5-1 K). The standard deviations of observed minus RTM-simulated radiances are between 0.5 and 1.5 K. Prior to data assimilation, these biases are corrected using a variational bias correction scheme. The largest impacts on the analyses, when assimilating imager radiances, are found in the mid- and upper-tropospheric moisture, while assimilation of sounder radiances impacted both moisture and temperature throughout the troposphere. The more accurate analyses with the INSAT-3D radiance assimilation lead to improved moisture, wind, temperature and precipitation forecasts compared to the control case in which only conventional observations were assimilated. The results demonstrate the ability of temperature- and water vapour-sensitive radiances to improve not only the temperature and moisture fields, but also the wind fields, enhancing their importance, particularly over tropical regions where wind observations are more important. © 2015 Royal Meteorological Society.

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