Upper tropospheric humidity from SAPHIR on-board Megha-Tropiques

Upper tropospheric humidity (UTH) has been derived using a ‘brightness temperature (Tb) transformation’ method from the humidity sounder channels of SAPHIR payload on - board Megha - Tropiques (MT). These channels are very close to the water vapour absorption peak at 183.31 GHz. The channel at 183.31 0.2 GHz enables retrieval of humidity up to the hig h est altitude possible wit h the present nadir - looking microwave humidity sounders. Megha - Tropiques satllite has an equatorially inclined orbit, which e n sures frequent spatial and temporal coverage of the global tropical belt. Transformation coeff i cients for the first three channels for all the incidence angles have been derived and are used to convert brightness temperatures to weighted average upper tropospheric humidity having weighting function peaks at different pressure levels. The methodology has been validated by comparing the SAPHIR - derived UTH with that derived from radiosonde observations. Inter - comparison of the derived UTH has been done with layer averaged humidity product from SAPHIR measurements and with UTH product using infrared measurements from Kalpana satellite ( MOSDAC). UTH over the tropical belt for six months has been studied taking the advantage of the humidity product with high spatial and temporal resolution. The transformation coefficients and methodology to identify the cloud - free pixels to derive UTH from the three channels for all the possible incidence angles are presented here, so that the users can directly derive UTH from the brightness temperature data

MT-MADRAS brightness temperature analysis for terrain characterization and land surface microwave emissivity estimation

This article reports the potential of the ‘MADRAS’ payload on-board the Megha-Tropiques satellite for land surface studies. The analysis has been divided into two parts as application of MADRAS data for studying the land surface properties and estimation of microwave emissivity directly from MADRAS brightness temperature (TB) data by applying an in-house developed Microwave Radiative Transfer Computation Code. The derived emissivity is further used to characterize the microwave emissivity of different land surface classes. The polarization difference (PD) parameters, the difference between horizontal (H-) and vertical (V-) polarization of TBs at 18 and 36 GHz clearly discern surface features of different surface classes such as deserts, arid/semi-arid an d vegetated regions. Land surface microwave emissivity for MADRAS channels is derived on a global basis. These are inter-compared with the emissivity derived from the operational TRMM Microwave Imager and are in reasonably good agreement. The analysis based on emissivity shows spectral variation for different surface classes

Tropical convective cloud characterization using ground-based microwave radiometric observations

Characterization of the microphysical and thermodynamical properties of convective events over the tropical coastal station Thiruvananthapuram (TVM) has been carried out based on multiyear microwave radiometer profiler observations. The analyses have been extended to develop a methodology to identify convective events, which is based on the radiometric brightness temperature (Tb) difference threshold, at 30 and 22.23 GHz channels, and the results are compared with reflectivity and rainfall intensity deduced from concurrent and collocated disdrometer measurements. Eighty-four of such convections were identified using the aforementioned methodology over the station during 2010-2013, i.e., both for pre- and post-Indian summer monsoon months, and further evaluated by computing their stability indexes. The occurrence of convective systems peaks in the afternoon and early-morning hours with genesis, respectively, over the land and the sea

Retrieval of Surface Emissivity of Sea Ice and Temperature Profiles over Sea Ice from Passive Microwave Radiometers

Polar regions play a key role in the global climate. The information on atmospheric parameters in these regions is sparse. Among the polar surfaces, sea ice varies in extent and physical properties with region and season and so does the surface emissivity. In the present study a method to retrieve the emissivity is applied over two selected regions in the Arctic, one covered by first-year ice and the other by multiyear ice and it investigates the application of them in the improvement of temperature profile retrieval ver sea ice. The retrieval of surface emissivity is done by combining simulated brightness temperatures with the satellite measured brightness temperature. In order to determine the surface emissivity of sea ice, the observations of the microwave instruments amsu (Advanced Microwave Sounding Unit) and amsr-e (Advanced Microwave Scanning Radiometer- Earth Observing System) are used. Determination of emissivity requires the knowledge of the temperature of the emitting layer. The penetration depth of microwaves in sea ice varies between millimeters and decimeters depending on the frequency and micro-physical structure. A year-round observation of temperature profiles of sea ice from the Surface Heat Budget of the Arctic Ocean (sheba) campaign at a first-year and a multiyear ice site is used to derive a set of coefficients a and b to linearly relate the lowest level air temperature and the different emitting layer temperatures. The method accounts for the variation of the penetration depthwith frequency, air temperature and sea ice temperature. An algorithm to retrieve temperature profiles from amsu data is modified using the retrieved emissivities and the derived temperature correction factors so that the retrieval accuracy of temperature profiles over sea can be improved

Bestimmung der Oberflächenemissivität von Meereis und Temperaturprofilenüber Meereis aus Daten passiver Mikrowellenradiometer.

Polar regions play a key role in the global climate. The information on atmospheric parameters in these regions is sparse. Among the polar surfaces, sea ice varies in extent and physical properties with region and season and so does the surface emissivity. In the present study a method to retrieve the emissivity is applied over two selected regions in the Arctic, one covered by first-year ice and the other by multiyear ice and it investigates the application of them in the improvement of temperature profile retrieval ver sea ice. The retrieval of surface emissivity is done by combining simulated brightness temperatures with the satellite measured brightness temperature. In order to determine the surface emissivity of sea ice, the observations of the microwave instruments amsu (Advanced Microwave Sounding Unit) and amsr-e (Advanced Microwave Scanning Radiometer- Earth Observing System) are used. Determination of emissivity requires the knowledge of the temperature of the emitting layer. The penetration depth of microwaves in sea ice varies between millimeters and decimeters depending on the frequency and micro-physical structure. A year-round observation of temperature profiles of sea ice from the Surface Heat Budget of the Arctic Ocean (sheba) campaign at a first-year and a multiyear ice site is used to derive a set of coefficients a and b to linearly relate the lowest level air temperature and the different emitting layer temperatures. The method accounts for the variation of the penetration depthwith frequency, air temperature and sea ice temperature. An algorithm to retrieve temperature profiles from amsu data is modified using the retrieved emissivities and the derived temperature correction factors so that the retrieval accuracy of temperature profiles over sea can be improved

Flood extent analysis over the major river basins in the Indian subcontinent using satellite microwave radiometric data

Every year South Asia suffers from widespread floods along its major river basins, especially during the southwest monsoon season calling for planning, mitigation, and hazard management strategies. This study demonstrates the application of land surface microwave emissivity data in identifying and quantifying flooded areas. It employs an indigenously developed scheme based on microwave radiative transfer to retrieve emissivities at 19 GHz from satellite microwave radiometers and to estimate emissivity polarization index ($EPI$) from it. By assigning thresholds to the $EPI$ for delineating inundated areas, this study examines the inter-annual variability of floods over the Indo-Gangetic plains for the period 2007–2010 and the cataclysmic flood of 2010 in Pakistan

A detailed study of land surface microwave emissivity over the Indian subcontinent

Microwave emissivities of land surfaces on global basis have been derived using Special Sensor Microwave/Imager brightness temperature data. These derived emissivities are compared with other reported emissivity values to demonstrate the accuracy of the retrievals. Following these results, detailed analyses on the microwave emissivities of the Indian subcontinent are carried out using the monthly mean emissivity estimate for two years. The Indian subcontinent has a wide variety of geographic and biospheric classes with distinctly different emissivity characteristics. The spectral and monthly variations of microwave emissivity for different tropical land surface classes are examined. This study is significant for microwave radiance assimilation in weather forecast models and also for the utilization of the data from passive microwave sensors onboard the Indo-French satellite “Megha-Tropiques,” which is dedicated to tropical atmospheric studies

Microwave radiometer observations of interannual water vapor variability and vertical structure over a tropical station

The intraseasonal and interannual characteristics and the vertical distribution of atmospheric water vapor from the tropical coastal station Thiruvananthapuram (TVM) located in the southwestern region of the Indian Peninsula are examined from continuous multiyear, multifrequency microwave radiometer profiler (MRP) measurements. The accuracy of MRP for precipitable water vapor (PWV) estimation, particularly during a prolonged monsoon period, has been demonstrated by comparing with the PWV derived from collocated GPS measurements based on regression model between PWV and GPS wet delay component which has been developed for TVM station. Large diurnal and intraseasonal variations of PWV are observed during winter and premonsoon seasons. There is large interannual PWV variability during premonsoon, owing to frequent local convection and summer thunderstorms. During monsoon period, low interannual PWV variability is attributed to the persistent wind from the ocean which brings moisture to this coastal station. However, significant interannual humidity variability is seen at 2 to 6 km altitude, which is linked to the monsoon strength over the station. Prior to monsoon onset over the station, the specific humidity increases up to 5–10 g/kg in the altitude region above 5 km and remains consistently so throughout the active spells