Difference in observation of Indonesian fire by DMSP-OLS and NOAA-AVHRR
Sensor Characteristics
DMSP-OLS
The DMSP-OLS has a unique capability to detect low levels of visible-near infrared (VNIR) radiance at night. With the OLS "VNIR" band data it is possible to detect clouds illuminated by moonlight, lights from cities, towns, industrial sites, gas flares, and ephemeral events such as fires and lighting illuminated clouds (Elvidge, et. al., 1997). Spatial resolution of DMSP-OLS is 2.7 km, and swath is 3000 km. DMSP-OLS is supposed to have advantages over other sensors in fire detection, for cloud cover in nighttime is generally less than in daytime. Moreover, DMSP-OLS could detect fire flares even through thin cloud or haze thanks to very high sensitivity of the sensors in VNIR band. A disadvantage of the DMSP-OLS sensor is that nighttime data may be obtained only for eight days each before or after new moon. It is because the VNIR sensor causes saturation when the ground surface is lit with moonlight.
NOAA-AVHRR
AVHRR is a canning radiometer on board NOAA's Polar Orbiting Environmental Satellite (POES) which measure reflected and emitted radiation at approximately 1 km spatial resolution, with swath of 2700km, in five channels ranging from 0.5 to 12.5
mm. Sub-pixel temperature targets can be identified in the short wave infrared data (channel 3 in AVHRR) during nighttime because these feature have greater effect in the 3.5-4.0
mm wavelength than in the longer wave infrared bands.
Data used for Analysis
The period from 26 October to 7 November 1997 was chosen for this study, for fairly cloud-free DMSP-OLS data were obtained almost everyday in this period. Cloud-free NOAA-AVHRR nighttime data of this study area were captured on 26 October, 31 October, 3 November, 4 November, and 7 November. The amount of available cloud-free data suggests that DMSP-OLS is superior to NOAA-AVHRR in terms of availability of data suitable for fire detection.
Methodology
The procedure used for this study is as follows : (a) "Hot spots" were identified with NOAA-AVHRR nighttime data by the improved contextual algorithm (Nakayama, et. al., 1998). (b) Fire flares were identified as faint "light" in imagery of DMSP-OLS using the methodology as described in (Elvidge, et. al., 1997) (c) Both "hot spots" detected by NOAA-AVHRR and "fire flares" by DMSP-OLS were compared for cloud-free areas. (d) Relative advantages and disadvantages of two sensors were evaluated.
