Active fire monitoring with level 1.5 MSG satellite images

American Journal of Applied Sciences, Jan, 2009 by Abdelatif Hassini, Farid Benabdelouahed, Noureddine Benabadji, Ahmed Hafid Belbachir

INTRODUCTION

The current generation of geostationary METEOSAT (Meteosat Second Generation, MSG) has 12 channels with a horizontal resolution of 3 km at the Sub-Satellite Point SSP and an image scan rate of 15 min. For the MSG, an algorithm for active fire monitoring has been developed (Active Fire Monitoring Algorithm, AFMA). This algorithm makes use of the MSG channels, in particular of channels Ch4 (IR 3.9) and Ch9 (IR10.8). Table 1 shows the characteristics of the twelve MSG-SEVIRI channels.

Table 1: Characteristics of the MSG-SEVIRI channels

Channels     Central wavelength ([mu]m)  Spectral band ([mu]m)

Ch1                   0.635                           0.56-0.71
Ch2                   0.810                           0.74-0.88
Ch3                   1.640                           1.50-1.78
Ch4                   3.920                           3.48-4.36
Ch5                   6.200                           5.35-7.15
Ch6                   7.350                           6.85-7.85
Ch7                   8.700                           8.30-9.10
Ch8                   9.660                           9.38-9.94
Ch9                  10.800                          9.80-11.80
Ch10                 12.000                         11.00-13.00
Ch11                 13.400                         12.40-14.40
HResVis               0.750                         Broadband visible

Each raw image received from the MSG satellite is radiometrically calibrated. The objectives for the radiometric calibration of the level 1.5 images are:

* To assure a linear relation between radiance and counts

* To assure an equalised response among detectors

* To apply the derived or received calibration information to the image data, therefore supplying a stable radiance-to-count relation for the level 1.5 data

The first two points refer to a pure relative calibration where the absolute relationship between counts and radiance is not considered, but rather that the detector output is linear and homogeneous over the whole image. The third point refers to the absolute calibration (1).

Forest and vegetation fires have typical temperatures in the range of 500-1000[degrees]K.(2). According to Wien's Displacement Law, the peak emission of radiance for blackbody surfaces of such temperatures is at around 4 [micro]m (MSG channel [Ch.sub.4] (3). For an ambient temperature of 290[degrees]K, the peak of radiance emission is located at approximately 11 [micro]m (MSG channel Ch9. Active fire detection algorithms from remote sensing use this behaviour to detect hot spot fires. MSG fire monitoring algorithms are typically using the combination of measured brightness temperatures in channels Ch4 and Ch9, their differences and their standard deviation over a 3x3 pixel array. Anyway, the main signal for active fires is an increase of the observed brightness temperature in channel Ch4, compared to the ambient temperature of the neighbouring pixels. The sensitivity of the channel Ch4 to hot spots is so high that it shows small sub-pixel fires, which do not have any significant impact upon the Ch9 temperature. However, the measurements in channel Ch4 can be attenuated or misled by [CO.sub.2] and water vapour absorption, solar reflectance during day and sub-pixel clouds over hot surfaces (4), (5).

The developed algorithm is named AFMA (Active Fire Monitoring Algorithm) tries to filter out the active fires by a combination of threshold tests using channels Ch4 and Ch9. The algorithm and its limitations are described in this research.

MATERIALS AND METHODS

The spinning enhanced visible and infrared imager (SEVIRI): The main components of active fire remote sensing comprise the remotely sensed (e.g., MSG-SEVIRI) data and the AFMA algorithm used to detect fire pixels from the data.

The overall Spinning Enhanced Visible and Infrared Imager (SEVIRI) layout is based on a compact three-mirror telescope and scan assembly. The 42 detectors of the twelve channels are accommodated in the telescope's focal plane in two areas, one at 20[degrees]C for solar channels (centred at wavelengths around 0.6, 0.8, 1.6 [micro]m and about 0.75 [micro]m for High Resolution Visible (HResVis) channel. The thermal infrared detectors (centred at wavelengths around 3.9, 6.2, 7.3, 8.7, 9.7, 10.48, 12.0 and 13.4 [micro]m) are passively cooled down (85[degrees]K or 95[degrees]K) to optimise their performance. The compact design allows the insertion of a small black body for full-pupil calibration. The response by every detector to the target's radiation is converted into an electronic signal by means of pre-amplifiers and a main detection unit. The amplification can be adjusted to the needs a various stages of the signal processing. The full image processing from raw counts to level 1.5 images is performed by the IMage Processing Facility (IMPF) branch of EUMETSAT (6).

MSG-1 and MSG-2 receiving station:

Hardware: To receive MSG-1 and MSG-2 data from the EUMETSAT (EUropean organization for the exploitation of METeorological SATellites) DVB (Digital Video Broadcasting ) Service, a complete DVB system is installed in our Laboratory and comprise a satellite receiving dish to be mounted outside, an LNB (Low Noise Block) which converts the 11GHz signal down to the 1GHz region and amplifies it to overcome cable loss, good satellite cable terminated with F-connectors to connect the LNB to DVB card and the DVB card itself which fits into one of the PCI slots inside a Personal Computer. Note that a 5-volt PCI slot is required. For Meteosat-8 and Meteosat-9 Eumetsat recommend that to have a separate PC dedicated to data capture and file sharing and that it should be at least a 2 GHz Pentium IV system or equivalent. For data capture, we have currently using a Pentium IV (3 GHz) machine as Receiver PC. We used in our case Windows XP system. The length of the cable from LNB to PC is about 20 m. Figure 1 shows synoptic of the acquisition system that we have installed (7), (8).