RESEARCH COMMUNICATIONS CURRENT SCIENCE, VOL. 113, NO. 1, 10 JULY 2017 112 *For correspondence. (e-mail: prakash@sac.isro.gov.in) SWIR albedo mapping of Mars using Mars Orbiter Mission data Ramdayal Singh 1,2 , Manoj K. Mishra 1 and Prakash Chauhan 1, * 1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 005, India 2 Faculty of Science, NIRMA University, Ahmedabad 382 481, India Global apparent short wave infrared (SWIR) (1.64– 1.66 m) albedo mapping results from data acquired by Methane Sensor for Mars (MSM) onboard Indian Mars Orbiter Mission from October 2014 to February 2015, are presented. Global analysis of low and high albedo patterns is discussed using MSM apparent SWIR albedo map. The occurrence frequency of MSM apparent SWIR albedo shows a clear bimodal behav- iour and is in good agreement with OMEGA NIR albedo distribution. Based on MSM apparent SWIR albedo values, three classes (high, intermediate and low albedo values) are defined, which show a clear elevation dependency. Variation of weekly average apparent albedo during the study period over Syrtis Major, Daedalia Planum and Valles Marineris region, respectively, is presented. Keywords: Albedo, Mars, methane sensor for Mars. THE Martian surface albedo mapping has remained an object of interest for the Earth-based astronomers for cen- turies. A number of surface markings of Mars have been produced using improved telescopic observation, which enable observers to assign relative quantitative albedo to major features. However absolute calibration of albedo was not possible 1,2 . In the last three to four decades the Martian surface albedo mapping has considerably improved when spacecrafts carried the high-resolution imaging systems to the Mars. The magnitudes and spatial distributions of Martian surface albedo are important inputs for a variety of interdisciplinary studies of Mars. Surface albedo, i.e. the fraction of solar incident light reflected into the atmosphere from the Martian surface acts as a driving force for meteorological systems, thus providing important boundary conditions for global circu- lation model (GCM) calculations. The meteorological conditions in turn place constraints on present and future spacecraft and mission designs. Various Mars missions have provided the albedo maps of Mars at different wave- length ranges, e.g. Infrared thermal mapper IRTM (20 m) albedo map from Viking mission 3,4 ; infrared im- aging spectrometer (ISM) albedo map from Phobos 5,6 ; 1 m Martian surface reflectivity map from spectroscopic observations in 0.3 m to 50 m (ref. 7); Hubble Space Telescope (HST) Mars’ reflectivity at 1.042 m (ref. 8); Mars Global Surveyor Thermal Emission Spectrometer (TES) derived albedo map 9 ; Mars Orbiter Laser Altimeter (MOLA) derived reflectivity of Mars using active sound- ing 10 ; and The Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité OMEGA near-infrared (NIR) (1.08 m) derived albedo 11 , MOLA derived reflectivity of Mars using passive radiometry 12 and MOLA derived re- flectivity of Mars using active and passive radiometry 13 . All of the albedo maps derived from different Mars mis- sions at different times show variations in albedo due to variability in the atmosphere of Mars associated with the seasonal transport of dust. In the present paper we have presented the global apparent short wave infra-red (SWIR) (1.65 m) albedo map derived from data acquired by Methane Sensor for Mars (MSM) onboard Indian Mars Obiter Mission (MOM) from October 2014 to February 2015. Based on correlation of global MSM apparent SWIR albedo with elevations, the Martian surface has been classified into three classes (high, intermediate and low albedo regions) and the occurrence frequency of these classes with re- spect to elevation is discussed. Comparative analysis of low and high albedo patterns is discussed using MSM SWIR and OMEGA NIR derived albedo maps. Apparent albedo variation with respect to solar longitude is repre- sented over Syrtis Major, Daedalia Planum and Valles Marineris regions, respectively. Methane Sensor for Mars (MSM) that has been developed at Space Applications Centre of the Indian Space Research Organisation (ISRO) aims to measure methane in Martian atmosphere with parts per billion (ppb) accuracy and map its resources. The mission has a highly elliptical orbit of 372  80,000 km that facilitates both localized observations with higher spatial resolution as well as observations with large coverage and high radiometric and temporal resolutions. The instrument is designed as a differential radiometer in SWIR region of the electromagnetic spectrum with a spectral range of 1.64 to 1.66 m (ref. 14). MSM measures reflected solar radiance in two SWIR (1.64 to 1.66 m) channels. There is absorption by CH 4 in the first channel (methane chan- nel) and no absorption in the second spectral channel (reference channel). The salient features of MSM are tabulated in Table 1. Table 1. Salient features of methane sensor for Mars Parameter Value Resolution (km) 0.63 at Periareion and 135 at Apoareion Swath (km) 4.4 at Periareion and 948 at Apoareion Spectral region 1.64 m to 1.66 m Integration time (ms) 0.25, 0.5, 1 and 2 (selectable) Quantization (bits) 20 (internally binned) Data rate (Mbps) 2.1875