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

Damen, M. C. J.

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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:: 1 Visible and infrared data. Chairman: F. Quiel, Liaison: N J. Mulder

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Airphoto map control with Landsat - An alternative to the slotted templet method. W. D. Langeraar

Document type:: Multivolume work

Structure type:: Chapter

lines (cut through the jungle after the photos are flown), can be exactly reconstructed. Considering the quality of the provided airphotos in terms of variations in scale and tilt, the slotted templet method was in this case found to yield unsatisfactory results, even though the assembly of templets was fitted to pass-points identified and linked to traverses by Euroconsult's topographical team. Although the location and orientation of each individual airphoto was in theory in this way fixed relative to the planimetrie map of traverses, in actual fact it appeared that locations of field observations could not always be traced back. This was especially valid for parts of the terrain remote from pass-points. 2.2 Use of Landsat Since the Australian Landsat Station (ALS) went on stream early in 1981, ample coverage by Landsat MSS imagery of southern Irian Jaya has become available. Although Landsat has been around since 1972, up to the establishment of ALS only a one-time acquisition of the region existed and then mostly covered with clouds. In recent years, however, consultants operating in the area have had at their disposal more and more cloud-free Landsat MSS imagery to complement and connect the existing scattered blocks of aerial photography. As will be shown below, with this development the most important mapping constraint mentioned above was overcome by Euroconsult. Landsat MSS bulk processed photographic products appeared sufficiently true to scale and shape as to serve as planimetric control for the construction of airphoto-derived basemaps. 3 THE SLOTTED TEMPLET METHOD 3.1 Principles The method is based on the assumption that directions to objects, when reckoned from the centre of a vertical aerial photograph, are constant under all conditions of elevation difference and scale change. Under this principle a scale adjustment can be made for a block of photographs by allowing corresponding points on adjacent airphotos freedom of movement away from and towards their centre points. The block of airphotos can thus be adjusted to scale, by making it fit a number of control points (Slama et al, 1980). The slotted templet method is a mechanical solution based on this principle. Although this method is obsolete as regards modern photogrammetric triangulation, in practice the slotted templet method is often still used in the field as the best option open to achieve a more or less usable result (depending on the quality of the photography). 3.2 Conditions for use A prerequisite for the proper working of slotted templet method is that the centres (principal points.) should more or less coincide with the nadir points of the airphotos. Another condition is that the individual scales of the photos should not fluctuate too much. In other words, the aerial photographs should be flown carefully, with minimum tilt and altitude variations. Unfortunately, this is not always the case with aerial photography made available to consultants working in developing countries. In addition to the fact that tilt and scale variations hamper the use of the slotted templet method, the method also requires a tremendous amount of time and patience to physically assemble the entire set of templets. 4 THE LANDSAT AIRPHOTO MAP CONTROL METHOD 4.1 Principle The principle on which the Landsat airphoto map control method is based, is the merging of Landsat's high planimetric accuracy over large areas, with the high local detail of aerial photographs. Ideally, merging of these two characteristics is best done by registration of the airphoto onto the Landsat scene with a rectifier. Next, the settings which compensate tilt and scale are freezed. Finally, the airphoto is blown-up to basemap scale. Though airphoto and Landsat can be matched optimally in this way, the procedure clearly is not suited for application under field conditions. As a result, we have resorted to an approach in which corresponding control points are sought on Landsat scene and airphotos. This basically approximates the above procedure. It is this technique that is described in the next Section. 4.2 Description The following is a step-by-step guide on how to use Landsat in combination with airphotos to produce a basemap under field conditions. * A Landsat scene covering the area of study is ordered in a conveniently large scale. (At ALS, 1/I6th of an MSS scene can be ordered at a scale of 1/50 000 in false-colour, with excellent results.) The date of aquisition should be close to that of the aerial photography to facilitate the next step. * Salient landmarks discernible on both airphoto and Landsat are pinpointed and allocated a number. * Temporary and arbitrary x-y coordinates of the points, scaled off the Landsat scene with the aid of translucent millimetre grid on a stable base, are multiplied by the scale ratio factor so that the points can be plotted on the basemap scale (nominal photo scale). The resulting matrix of points serves as a field of control points for the assembly of the air photographs in a map. * A minimum of three control points per airphoto is required in order to correct not only scale but also tilt variations. More than three control points enable a better check on compatibility between Landsat and corresponding airphoto points and increase the matching accuracy between Landsat and airphoto. * In actual practice an optical pantograph can best be used to mate the control points on the airphotos with their corresponding points on the basemap. Pantographs that allow the introduction of a certain amount of distortion are to be preferred (e.g. the Stereo Facet Plotter by O.M.I.) as they make it possible to approximately adjust for obliquity. * Using this instrument the principal points of the photographs can be transferred to the basemap, including all relevant geographic information visible on the aerial photographs. The resulting map contains pertinent, highly detailed, geographic information true to scale and

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