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MODIS — The old firewatcher

Akham Bonbirdhwaja Singh

The wildfires have been troubling the whole world from far east to down south, cold temperate forests of the North to tropical forests, dry African savannahs to rainforests all over the earth, there has been wildfires. Wildfires have claimed thousands of lives and billions worth property and resources. The wildfires have pumped in hundreds of gigatonnes of GHGs, they are accelerating the global warming. It is posing a great threat to mankind’s survival on earth. For keeping track of the wildfires for control and mitigation a close watch and monitoring is required. Due to its high temporal resolution and wide swath having maximum coverage and due to its specially designed functionality for observing changes on the ground and lower atmosphere, MODIS was highly suitable to be a firewatcher for us. The name MODIS had been quite a popular name in forest fire management for over a decade.
The MODIS or the MODerate-resolution Imaging Spectroradiometer is a remote sensing system which belongs to NASA (National Aeronautics and Space Administration) and it was launched in to the earth orbit in 1999 on board the Terra satellite and again on board Aqua Satellite in 2002. This Spectroradiometer capture data from earth in 36 spectral bands of 0.4 µm to 14.4 µm wavelength. The designed spatial resolutions are 2 bands in 250m, 5 bands at 500m resolutions and 29 bands at 1km. The MODIS’s satellites are stationed at 705 km altitude and together MODIS instruments can image the entire earth in 1-2 days time and takes 98 minutes to complete an orbit. One of the satellite passes over India in every six hours and hence, it is possible to see the changes in the morning and evening again. MODIS utilizes four on-board calibrators in addition to the space view in order to provide in-flight calibration: solar diffuser (SD), solar diffuser stability monitor (SDSM), spectral radiometric calibration assembly (SRCA), and a v-groove black body.

At global level, the data sets of MODIS have been effectively engaged for various purposes including fire management. For India, the Forest Survey of India (FSI) has been monitoring forest fire incidents through remote Sensing and GIS based Technology from 2004 to 20011. The FSI was doing near real time monitoring of forest fire through which forest fire alerts had been sent to State Forest Departments through SMS using a remote sensing based system developed by University of Maryland. In its efforts for forest fire monitoring, the FSI obtained the MODIS through NRSC (National Remote Sensing Centre) as NRSC has collaboration with NASA. From 2012 onwards FSI in collaboration with National Remote Sensing Centre (NRSC) has initiated a Real Time Monitoring of Forest Fire wherein the forest fire alerts from active fire locations are being generated as KML file which is Google compatible format. The alerts have been sent to registered users via Emails and SMS. The KML alert would be up to state level where as SMS alert would be up to District level. The Time lag of the information is less than 2 hours from the pass of satellite. The SMS alerts of the fire coordinates can be sent to the state Nodal Agency and District agency once it is registered with FSI. This a very advance system of fire monitoring and assessment. The FSI is providing such data free of cost to those registered users and there is no charge for registration also. Such data can also be used by the disaster managers and planners too.

The limitation in monitoring system developed with MODIS data has been few and not inherent with MODIS, but in the application the respective countries have designed. For example limitations in case of Manipur would be that the fire alerts are for the period of January to June only whereas in Manipur fire starts by November itself we would be missing a large chunk of data pertaining to November and December (Fire is quite prevalent in first and second week of December prior to Christmas). Secondly, many of forest fires of Manipur are surface fires of smaller scale which is beyond the spatial resolution of the MODIS’ satellite. Generally, MODIS can detect fires of 30m x 30m though the spatial resolution for high resolution band is 250m x 250m and medium resolution is 500m x 500m. The problem shall remain with the new incarnation of MODIS, the VIIRS also. So for comprehensive monitoring and assessment, a response mechanism need to be developed which could be quite expensive. Another limitation is that as fire is a dynamic entity moving as per slope of land and wind movement, this attribute is not captured by MODIS as the burnt area, once it does not emit heat after a period of time would not be detected by the thermal sensors of MODIS in the next cycle. This aspect would be much improved in VIIRS as it stationed on a higher orbit with wider swath. In the forest fire alerts, only point data is being sent to the field officers. Of course, this much of near real-time data is of immense value for monitoring of forest fire.

The MODIS was designed to last for 6 years and was launched in 1999 and 2002 and it has outlived its life span two times and it is still operational. Being aged, NASA had plans for second generation high temporal resolution satellite for detection of quick changes such as clouds, fire, tides etc. MODIS is to be phased out, it is succeeded by the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument on board the Suomi NPP satellite launched in 2011 and future Joint Polar Satellite System (JPSS) satellites (JPSS 1 shall be launching another VIIRS instrument next month, Nov 2017). It is believed that the temporal efficiency shall be more in VIIRS as its satellites are stationed higher at 829 km altitude (705 km of MODIS’ Aqua and Terra Satellites) and imaging swath width is 3060 km (2330 km of MODIS). However, the MODIS data set shall be still useful and using combined with VIIRS data set, comprehensive assessment of climate change pattern and others for last twenty years shall be possible. MODIS would be phased out, but its legacy would not be gone, it would be carried on by the VIIRS because due to increased incidences of wildfires all over the world and threat of climate change looming large, firewatching is still required to make the earth safe for all of us.

(The writer can be reached at: bonbir01@rediffmail.com)

Source: The Sangai Express



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