Wolfgang Skrbek

HSRS: an infrared sensor for hot spot detection

The observation of high temperature events (HTE) is an important field of the remote sensing because of their influence on the global change of the environmental processes. Currently a small satellite BIRD (Bispectral Infrared Detection) dedicated to this task is under development in the German Aerospace Center. Considering the restrictions of an 80 kg satellite a bispectral infrared push broom scanner working in the Midwave and in the Thermal Infrared based on the latest technology of linear detector arrays was developed. The identical design for both infrared channels was realized to save resources and to guarantee the reliability. Because of the limited number of elements per line a subpixel detecting concept was chosen to estimate the parameters of the HTE with a reasonable ground resolution and swath wide. A special dual band optics and a compact sensor head design will ensure the required geometric stability. The subpixel measurement method for the hot spot detection requires a high detectivity and a large dynamic range. A special signal processing concept has been implemented at the sensor head controller. Recently the first airborne experiments were carried out together with a push broom scanner in the visible. During this experiments the sensor control, onboard signal processing and data transmission routines were tested.

BIRD detection and analysis of high-temperature events: first results

The primary mission objective of a new small Bi-spectral InfraRed Detection (BIRD) satellite, which was put in a 570 km circular sun-synchronous orbit on 22 October 2001, is detection and quantitative analysis of high-temperature events (HTE) like fires and volcanoes. A unique feature of the BIRD mid- and thermal infrared channels is a real-time adjustment of their integration time that allows a HTE observation without sensor saturation, preserving a good radiometric resolution of 0.1-0.2 K for pixels at normal temperatures. This makes it possible: (a) to improve false alarm rejection capability and (b) to estimate HTE temperature, area and radiative energy release. Due to a higher spatial resolution, BIRD can detect an order of magnitude smaller HTE than AVHRR and MODIS. The smallest verified fire that was detected in the BIRD data had an area of ~12 m2. The first BIRD HTE detection and analysis results are presented including bush fires in Australia, forest fires in Russia, coal seam fires in China, and a time-varying thermal activity at Etna.

Calibration of a bispectral infrared push-broom imager

In May 2001 was planned to launch the small satellite BIRD, but the launch was shifted to August/September 2001. The main payload is dedicated to the observation of high temperature events and consists mainly of a Bi-Spectral IR Push Broom Scanner and a Push Broom Imager in the Visible. Solid state detector arrays with adaptive high dynamic front end electronics and advanced digital signal processing capabilities are the key element of IR imaging devices. With respect to the main mission objectives besides the high radiometric requirements to the detectors their mutual geometrical alignment is essential. The main problem of the radiometric calibration is the required high dynamic range which makes necessary to consider the non linear characteristic of the detector elements. On the other hand the application of special bi-spectral methods requests a carefully geometrical calibration. Besides the alignment of the different spectral channels the knowledge of the PSF is necessary. The laboratory radiometric and geometrical calibration procedures are described in this paper.

Detection, monitoring, and quantitative analysis of wildfires with the BIRD satellite

Increasing concern about environment and interest to avoid losses led to growing demands on space borne fire detection, monitoring and quantitative parameter estimation of wildfires. The global change research community intends to quantify the amount of gaseous and particulate matter emitted from vegetation fires, peat fires and coal seam fires. The DLR Institute of Space Sensor Technology and Planetary Exploration (Berlin-Adlershof) developed a small satellite called BIRD (Bi-spectral Infrared Detection) which carries a sensor package specially designed for fire detection. BIRD was launched as a piggy-back satellite on October 22, 2001 with ISRO’s Polar Satellite Launch Vehicle (PSLV). It is circling the Earth on a polar and sun-synchronous orbit at an altitude of 572 km and it is providing unique data for detailed analysis of high temperature events on Earth surface. The BIRD sensor package is dedicated for high resolution and reliable fire recognition. Active fire analysis is possible in the sub-pixel domain. The leading channel for fire detection and monitoring is the MIR channel at 3.8 μm. The rejection of false alarms is based on procedures using MIR/NIR (Middle Infra Red/Near Infra Red) and MIR/TIR (Middle Infra Red/Thermal Infra Red) radiance ratio thresholds. Unique results of BIRD wildfire detection and analysis over fire prone regions in Australia and Asia will be presented. BIRD successfully demonstrates innovative fire recognition technology for small satellites which permit to retrieve quantitative characteristics of active burning wildfires, such as the equivalent fire temperature, fire area, radiative energy release, fire front length and fire front strength.

Design and analysis of a small bispectral infrared push broom scanner for hot spot recognition

A small bispectral infrared detection (BIRD) push broom scanner for a small satellite emission is described, which is dedicated to the detection and analysis of high temperature events (HTE). Current operating and planned satellite sensors are not designed for high temperature event observation and therefore show some serious drawbacks such as saturation of the IR channels for target temperatures higher than 50 degrees Celsius, low spatial resolution in case of daily coverage, low coverage of spatially high resolving systems, or not adequate IR channels. The BIRD instrumentation is a first attempt to overcome these disadvantages. For this purpose two infrared line scanners (3.4 - 4.2 micrometer and 8.5 - 9.3 micrometer) are combined with a wide angle stereo scanner (WAOSS) in the visible. Because of the limited resources of a small satellite the design of all instruments is based on the usage of staring focal plane arrays. To observe HTE directly the covered sounding area should be as large as possible whereas at first glance the ground resolution of the sensor should be in order of some 10 m. These demands are in contradiction with the number of the infrared detector array elements currently available. For this reason methods of subpixel target detection and analysis have to be used. According to this concept a combination of the data from at least to radiometric high sensitive infrared sensor channels is used to compensate the lack of high ground resolution. Adding to the infrared cameras a suitable CCD-line scanner for a pre-classification with a higher ground resolution, a marked improvement can be achieved.

Sensor system for fire detection on-board the small satellite BIRD

With the successful launch of BIRD satellite in October 2001, new possibilities of the observation of hot events like forest fires, volcanic eruptions a.o. from space are opened. The BIRD (Bi-spectral Infrared Detection) is the first satellite which is equipped with space instrumentation dedicated to recognize high temperature events. Current remote sensing systems have the disadvantage that they were not designed for the observation of hot events. Starting with the FIRES Phase A Study, the principle requirements and ideas for a fire recognition system were defined. With the German BIRD demonstrator mission, a feasible approach of these ideas has been realized and work now in space. This mission shall answer technological and scientific questions related to the operation of a compact bi-spectral infrared push-broom sensor and related to the detection and investigation of fires from space. The payload of BIRD is a multi-sensor system designed to fulfil the scientific requirements under the constraints of a micro satellite. The paper describes the basic ideas for fire detection and the estimation of fire temperature, fire size, and energy release in the sub-pixel domain and describes the technical solution for the infrared sensor system on board of BIRD.

The BIRD payload platform

For hot spot events as forest fires, volcanic activity or burning oil spills and coal seams a dedicate dspace instrumentation does not exist. With its successful launch end of October 2001 with the Indian Polar Satellite Launch Vehicle the German Aerospace Center starts closing this gap with the micro-satellite mission BIRD. As space segment serves a three-axis stabilized satellite of 92 kg including a contingent of over 30% for the scientific instruments. The main payload of the BIRD micro-satellite is the newly developed Hot Spot Recognition System. Its a dual-channel instrument for middle and thermal IR imagery based on cooled MCT line detectors. The miniaturization by integrated detector/cooler assemblies provides a highly efficient design. A complement for the hot spot detection is the wide-angle stereo-scanner WAOSS-B. It is a hardware re-use dedicated to vegetation and cloud assessment in the visible spectral range. Besides the main objective of hot spot detection the mission has to answer several technological questions of the operation of cooled detectors in space, special aspects of their adaptation to the satellite platform as well as their calibration.

Objectives and results of the BIRD mission

The DLR small satellite BIRD (Bi- spectral Infrared Detection) is successfully operating in space since October 2001. The main payload is dedicated to the observation of high temperature events and consists mainly of a Bi-Spectral Infrared Push Broom Scanner (3.4-4.2μm and 8.5-9.3μm), a Push Broom Imager for the Visible and Near Infrared and a neural network classification signal processor. The BIRD mission answers topical technological and scientific questions related to the operation of a compact infra-red push-broom sensor on board of a micro satellite. A powerful Payload Data Handling System (PDH) is responsible for all payload real time operation, control and on-board science data handling. The IR cameras are equipped with an advanced real time data processing allowing an autonomously adaptation of the dynamic range to different scenarios. The BIRD mission control, the data reception and the data processing is conducted by the DLR ground stations in Weilheim and Neustrelitz (Germany) and is experimentally performed by a low cost ground station implemented at DLR Berlin-Adlershof. The BIRD on ground data processing chain delivers radiometric and geometric corrected data products, which will be also described in this paper. The BIRD mission is an exemplary demonstrator for small satellite projects dedicated to the hazard detection and monitoring.

Thematic data processing on board the satellite BIRD

The general trend in remote sensing is on one hand to increase the number of spectral bands and the geometric resolution of the imaging sensors which leads to higher data rates and data volumes. On the other hand the user is often only interested in special information of the received sensor data and not in the whole data mass. Concerning these two tendencies a main part of the signal pre-processing can already be done for special users and tasks on-board a satellite. For the BIRD (Bispectral InfraRed Detection) mission a new approach of an on-board data processing is made. The main goal of the BIRD mission is the fire recognition and the detection of hot spots. This paper describes the technical solution, of an on-board image data processing system based on the sensor system on two new IR-Sensors and the stereo line scanner WAOSS (Wide-Angle-Optoelectronic-Scanner). The aim of this data processing system is to reduce the data stream from the satellite due to generations of geo-coded thematic maps. This reduction will be made by a multispectral classification. For this classification a special hardware based on the neutral network processor NI1000 was designed. This hardware is integrated in the payload data handling system of the satellite.

Airborne testing of a bispectral infrared pushbroom scanner for hotspot detection

A small Bi-spectral Infrared Detection (BIRD) push broom scanner for a small satellite mission is developed, which is dedicated to the detection and analysis of high temperature events (HTE) including the surrounding background scenario. To avoid the saturation of the detector at high temperatures keeping at the same time a reasonable radiometric resolution for the background a very large dynamic range is required, which will be realized by special adaptive sample techniques. These techniques were proved and verified during special airborne experiments. Using two cameras in different spectral regions (3.4 - 4.2 micrometer and 8.5 - 9.3 micrometer) with a well synchronized sampling mode, it is also possible to detect and analyze hot targets with an extension much less than the nominal ground pixel size. An excellent synchronization of the cameras is required to avoid time expensive matching procedures and therefore to enable a related real time processing. A pre-condition for these sub- pixel techniques is the recognition of the related areas distinguishing them from sun glints and similar false alarm candidates. Analyzing the data of the airborne experiments, the processing algorithms could be tested and improved.