Remote sensing for resources development and environmental management: Remote sensing for resources development and environmental management

Damen, M. C. J.

Bibliographic data

Multivolume work

Persistent identifier:: 856342815

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856342815

Language:: English

Additional Notes:: Volume 1-3 erschienen von 1986-1988

Editor:: Damen, M. C. J.

Document type:: Multivolume work

Volume

Persistent identifier:: 856343064

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Scope:: XV, 547 Seiten

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856343064

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(26,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Damen, M. C. J.

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: 3 Spectral signatures of objects. Chairman: G. Guyot, Liaison: N. J. J. Bunnik

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: A preliminary assessment of an airborne thermal video frame scanning system for environmental engineering surveys. T. J. M. Kennie & C. D. Dale, G. C. Stove

Document type:: Multivolume work

Structure type:: Chapter

286 3 THERMAL VIDEO FRAME SCANNERS (TVFS) A TVFS system consists of four basic components: (a) a scanning system which views the scene to be imaged and focusses the incoming infrared radiation, (b) a ferro-magnetic or semi-conductor detector which measures the thermal variations in the scene, (c) a CCTV compatible display system where the thermal variations are used to modulate the intensity of an electron beam, and (d) a video cassette recorder (VCR) to record the thermal imagery. Unlike thermal IR linescanning systems which are designed specifically for airborne use, the TVFS systems under consideration are designed for both ground and airborne operation. Consequently, the optical configuration, scanning mechanisms and detector arrays differ from those used for thermal linescanning and this leads to significantly different imaging systems being employed. 3.1 Imaging techniques In general terms a thermal imager operates by mechanically scanning a focussed beam of incoming radiation onto an infrared detector. In its simplest form, such as in a thermal IR linescanner, the scanning is performed in one direction, perpendicular to the direction of flight, by an oscillating mirror or rotating prism. The incoming radiation is then focussed onto a single detector, normally of mercury cadmium telluride (HgCdTe). The 'frame' scanning in this case is performed by the forward motion of the aircraft. If the imager is to be used from, a static platform then some method of scanning in two dimensions is required. There are, however, several practical difficulties with such a single element detector design if a flicker free, high spatial resolution image is to be obtained. Consequently, if high resolution is required it is often more efficient to use a multi-element detector design. Three distinctive arrangements are possible: parallel, serial and matrix scanning. Parallel scanning involves using a single column of detectors arranged so that each detector element scans a single line in the image. This arrangement reduces the scanning speed. However, the performance of each of the detector elements needs to be similar if the formation of a 'streaky image' is to be avoided. Further significant reductions in scan speed can also be achieved by using band interlaced scanning techniques (Chiari and Morten, 1982). Serial scanning systems, in contrast, operate by using a single row of detector elements. The cumulative output is obtained by summing the individual signals from each detector. In order to achieve this it is necessary to include separate pre-amplifiers and delay line circuitry for each detector element. Although the electronics of this design are more complex, since the same detector element scans all lines in the image the uniformity of the image is more consistent than with the parallel system. A compromise arrangement which combines the scene uniformity advantages of the serial scan approach with the high scan speeds of the parallel arrangement is the mixed parallel/serial or 'matrix' design. Inevitably, as the number of detector elements increases, so the number of electrical connections also increases. Although this difficulty, and the consequent signal processing complications can be overcome, the design trend in recent years has been to use SPRITE detectors. As mentioned previously, with conventional serial scanning the output from each IR detector is pre-amplified, delayed and then added to the signal which is generated in the following element. SPRITE (Signal PRocessing In The Element) detectors overcome the need for these separate connections. In the SPRITE design the row of individual detectors is replaced by a single strip of HgCdTe with only two connections and one pre-amplifier. Eight element SPRITE detectors are used in most TVFS systems, such an arrangement is equivalent to a conventional array consisting of 64 discrete elements. Although SPRITE detectors eliminate many of the connections and much of the circuitry, they still require some form of mechanical scanning to be carried out. An area of considerable interest at present is the development of 'staring arrays' i.e. a matrix of infrared detectors. In this case the function of the optics is simply to focus the incoming radiation onto the matrix of detectors located in the focal plane of the camera. Whilst it is likely that such arrangements will eventually replace the SPRITE design, this is unlikely to occur until very dense matrices can be formed thus enabling high resolution imagery to be produced. 3.2 System review A wide range of thermal imaging systems are currently available and Table 2 outlines the technical specifications associated with a selected sample. Table 2: Technical Specifications : Thermal Video Frame Scanning Systems. Spatial Resolution (mr) MRTD* (°C) Spectral Range (pm) AGA Thermovision 5.8 0.1 3-5.6 8-12 GEC V1010 TICM 11 2.27 0.1 8-13 Hawkeye HT4 2.1 0.15 8-13 Rank Pullin Controls SS600 2.1 0.15 8-13 Infremetrics IRTV-445G 2.0 0.4 8-12 FLIR Systems 1000A 1.87 0.2 8-12 Barr and Stroud IR18 1.73 0.38 8-13 MRTD* = Minimum Resolvable Temperature Difference As mentioned in the literature review several previous authors have discussed the use of the AGA Thermovision range of instruments for airborne use. These instruments, of which model 782 is the most recent, are single detector, low spatial resolution systems. Two versions of this instrument are available for sensing in the 3 to 5 urn and 8 to 14pm regions of the spectrum. An image consisting of 100 elements/line over a 280 lines/frame format refreshed at 25Hz and interlaced four to one is produced by the scanner. In addition to the low spatial resolution of the instrument the slow refresh rate creates image registration problems when sensing from a moving platform. A further disadvantage is the difficulty of producing a vertical image. In order to achieve this a 45° mirror has to be used so as to avoid the liquid nitrogen from the cooling system being expelled. The Inframetrics IRTV 445G can however be gimbel mounted for airborne use. It uses a 4 element HgCdTe detector and creates a 400 elements/line image over a 445 lines/freme format refreshed at at a frame rate of 30Hz. developed enhancing temperatur The majo operating for avion the curren 1976 and a a modular Thermal Inr GEC V1010 Instrument fixed wing case the forward lc The Rank differs fr which uses elevation scan. In mounted rc scan patte claimed to compact in vibration MIRF INCC RADI Figure 1. (Lettingtc The Barr on a modu field of equivalenl optical-m< discussed 3.3 The В Frame Scai The scanm initial ly for commei outlines ! sensor am operation To achii criteria must be ri 625 line l to achievi a high sp

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