Remote sensing data (satellite-based data)

Different types of RS data were used in this study to estimate different meteorological variables and LULC information. All RS data that were used are described in the following sub sections.

MODIS data

Moderate Resolution Imaging Spectroradiometer data are the major set of RS data used in this study. MODIS is the predecessor of Advanced Very High Resolution Radiometer (AVHRR), and was developed for land, ocean and atmospheric applications at regional levels. MODIS provides better sensitivity to vegetation and other ground features because of its specific sensor characteristics (Thenkabail et al., 2004). The MODIS sensor acquires data on a daily basis in 36 spectral bands (Table 2.4), with variable spatial resolution of 250–1,000 meters. Bands 1 and 2 have a 250 m spatial resolution, bands 3 to 7 have a 500 m spatial resolution, and the remaining bands have a 1,000 m spatial resolution. These 36 MODIS bands are generally designed for atmospheric, land and ocean studies, but the first seven bands are considered optimal for land applications (Justice et al., 2002). MODIS was used in this study to acquire information on ground features such as vegetation, surface emissivity and surface temperature as well as brightness temperature of clouds. Both MODIS Terra and Aqua level 1 data were collected for this study from the Atmospheric Archive and Distribution System (LAADS) web portal of the National

Aeronautics and Space Administration (NASA)

(http://ladsweb.nascom.nasa.gov/data/search.html). However, MODIS data which are on the Terra platform were mainly used in this study, while any tilted and absent images from Terra were replaced with images from Aqua.

TRMM data

The Tropical Rainfall Measuring Mission is a unique program jointly designed and operated by the NASA and the Japan Aerospace Exploration Agency (JAXA) for the purpose of accurately measuring spatial and temporal variation of tropical rainfall. Both optical and microwave sensors are mounted in TRMM, and as such it can acquire information on the magnitude and spatio-temporal variation of precipitation as well as the latent heat over land and ocean (Pierce, 2008). This helps to understand the spatial variation of precipitation and its frequency, as well as the intensity of the precipitation. In

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addition, TRMM is used to understand the vertical distribution of hydrometeors, and the convective and monsoonal precipitation categories. TRMM acquires data on a daily basis. Based on these data, NASA and JAXA release various rainfall products with different spatial and temporal resolutions.

In this study, dataset 3B42 of TRMM Multi Satellite Precipitation Analysis (TMPA) was used to generate finer spatial resolution rainfall data. This dataset is 0.250x0.250 degrees in spatial resolution with three hour temporal resolution, and covers 500 N to 500 S of the globe. The 3B42 dataset is primarily a merged product of the microwave and infrared precipitation, which is then calibrated with rain gauge data (Huffman et al., 2007). The microwave data are based on Low Earth Orbital (LEO) satellite microwave sensors, and infrared data are based on Geosynchronous Earth Orbit (GEO) satellite sensors. The microwave sensor data (SSM/I, AMSU-E, AMSU-B and TMI) have higher spatial resolution but only cover 80% of the earth’s surface globe in the range of 400 north and 400 south from the equator per day (Huffman et al., 2007). However, GEO infrared data cover the entire globe every 30 minutes with 4 km x 4 km spatial resolution.

In the process of deriving 3B42, instantaneous microwave data are first used to estimate precipitation for the nearest three hour period (0000, 0300, …). It is then merged with infrared precipitation which is estimated separately. This fills the gaps of microwave precipitation estimates and gives seamless data coverage over the globe. Finally, the merged data are calibrated with TRMM precipitation radar, Global Precipitation Climatology Project (GPCP) monthly rain gauge analysis and Climate Anomaly Monitoring System (CAMS) monthly rain gauge analysis data (Huffman et al., 2007) to produce 3B42. This dataset (3B42) was downloaded at no cost for the entire duration of the study (2003 – 2008) from the Goddard Earth Science and Data Information Centre’s

web portal (http://mirador.gsfc.nasa.gov/cgi-

bin/mirador/presentNavigation.pl?tree=project&project= TRMM).

IGGC data

Infrared Global Geostationary Composite (IGGC) data (https://wist.echo.nasa.gov), which are available at every 30 minutes intervals, were used to estimate cloud cover in this study, which in turn were used to estimate evapotranspiration. IGGC data are a combination of several geostationary and polar orbiting satellite data, received from the Geostationary

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Satellite system (GOES), the Multi-Functional Transport Satellite (MTSAT), and the Meteosat and National Oceanic and Atmospheric Administration (NOAA). All of these data are from the infrared band (11 µm channel) of the aforementioned satellites. The geostationary satellites of GEOS, Meteosat and MTSAT cover the area surrounding the equator, while the NOAA satellite covers the Polar Regions (Goodman, 2011).

Landsat Data

Landsat data were used in this study to classify LULC, as its spatial resolution is sufficient to represent the ground heterogeneity of the study areas compared to MODIS data. Landsat data are also freely available compared to other competitors such as the Indian Remote Sensing (IRS) satellite data and SPOT (Système Pour l’Observation de la Terre) data. Landsat 5 (which was launched on 1 March 1984 and decommissioned on 5 June 2013) and Landsat 7 (which was launched on 15 April 1999 and is still operational) data can be downloaded from the internet.

Landsat 5 is equipped with a Thematic Mapper (TM), and has seven bands. Out of those seven bands, six bands which are visible and short wave infrared have 30 m spatial resolution, while the longwave infrared (thermal) band has 120 m spatial resolution (Lillesand and Kiefer, 1999). The revisit time of the Landsat 5 is 16 days, and Landsat data can be downloaded either from the NASA’s Earth Observing System Data and Information System (EOSDIS) web port (http://reverb.echo.nasa.gov/reverb/) or from the Global Land Cover Facility (GLFC) web port of University of Maryland (http://www.landcover.org/index.shtml).

3.3.1.2 Ground-based data