Sentinel hotspots are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board Terra (morning pass) and Aqua (afternoon pass) satellites. Images are captured, over a given point at least four times a day, between the two satellites, each with a ground swath of 2330 km and day/night coverage.
MODIS acquires data in 36 spectral bands, two of which are primarily thermal infrared channels at 4 and 11 µm and used for hotspot detection. The algorithm developed by the University of Maryland/NASA detects hotspots if T4 - T 11 ≥ 20K (10K for night passes) and T4 > 320K (315K for night passes), where, T4 and T11 represent brightness temperatures in degrees Kelvin derived from MODIS bands 22 and 31 respectively.
Additionally, contextual information such as average background temperature and sun-glint factor is also considered when detecting hotspots.
The accuracy of MODIS data is considered to be superior to Advanced Very High Resolution Radiometer (AVHRR) data when detecting hotspots because it has higher sensitivity and fewer temperature saturation problems.
The new system offers a number of improvements over the original system.
The response time has been reduced when updating hotspot information on the web. Originally taking 60 to 90 minutes after acquisition to process, it now takes 45 minutes for daytime passes and 20 minutes for night passes, resulting in an improved website performance.
The quality of the MODIS colour imagery (500m) has also improved and is now updated within two hours of acquisition. There is also a choice of access from dial-up to broadband internet connection.
MODIS data acquired from the Hobart ground station is now integrated into the web service, which extends the Sentinel hotspot coverage to New Zealand. It also serves as a "backup" for South East Australia and is in addition to the Alice Springs coverage.
The new find/search facility will allow users to find the location of bushfires using the area name or other attributes such as lakes, airports, etc. Users can also search bushfires within a given buffer zone.
The system also supports additional topographic data (250K maps) and offers interoperable web mapping and feature service.
More satellite data and hotspot information from other satellites such as AVHRR will be added progressively by Geoscience Australia. Importantly, both CSIRO and Geoscience Australia's Sentinel web services will run in unison until at least January 2006. Once the operational capability of Geoscience Australia's system has been established, CSIRO will then withdraw its' Sentinel web service.