The Megha-Tropiques mission: a review after three years in orbit

Abstract

International audienceThe Megha-Tropiques mission is operating a suite of payloads dedicated to the documentation of the water and energy cycles in the intertropical region in a low inclination orbit. The satellite was launched in October, 2011 and we here review the scientific activity after the first three years of the mission. The microwave sounder (SAPHIR) and the broad band radiometer (SCARAB) are functioning nominally and exhibit instrumental performances well within the original specifications. The microwave imager, MADRAS, stopped acquisition of scientific data on January 26th, 2013 due to a mechanical failure. During its 16 months of operation, this radiometer experienced electrical issues making its usage difficult and delayed its validation. A suite of geophysical products has been retrieved from the Megha-Tropiques payloads, ranging from TOA radiative flux to water vapor profiles and instantaneous rain rates. Some of these geophysical products have been merged with geostationary data to provide, for instance, daily accumulation of rainfall all over the intertropical region. These products compare favorably with references from ground based or space-borne observation systems. The contribution of the mission unique orbit to its scientific objectives is investigated. Preliminary studies indicate a positive impact on both, humidity Numerical Weather Prediction forecasts thanks to the assimilation of SAPHIR Level 1 data, and on the rainfall estimation derived from the Global Precipitation Mission constellation. After a long commissioning phase, most of the data and the geophysical products suite are validated and readily available for further scientific investigation by the international community

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

“…Because of mechanical issues, operation of MADRAS ceased after 15 months of observations (on January 26, 2013). A novelty of the Megha-Tropiques platform is its low inclination of 20 around the equator, which translates into a higher revisit frequency: The satellite orbits the tropics about fourteen times per day yielding between two to six observations per day at a given location between 25 N and 25 S. Further information about Megha-Tropiques is provided by Roca et al (2015) and Capderou (2009).…”

“…Channel 1 measures the line within AE0:2 GHz, Channel 6 within AE11 GHz, (Eymard et al 2002). Channel 1 is most sensitive to water vapor in the upper troposphere, near 300 hPa, Channel 6 is more sensitive to water vapor in the lower-troposphere, near 600 hPa (Roca et al 2015). By virtue of their differences, signals from these channels can be used to estimate relative humidity (in % with respect to liquid water) in six unevenly spaced layers of the atmosphere, as indicated in Table 1.…”

Evaluation of radar reflectivity factor simulations of ice crystal populations from in situ observations for the retrieval of condensed water content in tropical mesoscale convective systems

“…The principle of the technique is to retrieve CWC from simulations of radar reflectivity factors (Ze), calculated from OAP image information and compared to measured RASTA radar data. The data were collected in tropical MCSs that formed over the African continent and over the Indian Ocean during two aircraft campaigns dedicated to the Megha-Tropiques project (Roca et al, 2015). The main drawback of these experiments is that they do not include direct measurement of CWC.…”

Assessment of small-scale variability of rainfall and multi-satellite precipitation estimates using measurements from a dense rain gauge network in Southeast India

“…As part of one such satellite validation programMegha-Tropiques (Raju, 2013;Roca et al, 2015) -NARL established a dense network of rain gauges in 2011, covering an area of 50 × 50 km 2 centered around Gadanki. The network consisting of 36 rain gauges spreads from 78.9 to 79.4 • E and from 13.1 • N to 13.6 • E (Fig.…”

“…The objectives of this paper, therefore, are to quantify and understand the small-scale variability (spatial and temporal) of precipitation over a complex hilly terrain and also to validate high-resolution MPEs using a dense network of rain gauges established around Gadanki (13.45 • N, 79.18 • E). This network has been established as part of the Megha-Tropiques (an Indo-French joint satellite mission) validation program (Raju, 2013;Roca et al, 2015). This being the first paper on this network, its establishment and maintenance (stringent calibration procedures adopted) are also discussed briefly.…”