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

49 me and patience set of templets. ROL METHOD airphoto map rging of y over large of aerial aracteristics is irphoto onto the xt, the settings e freezed. to basemap can be matched re clearly is ield conditions, n approach in are sought on basically It is this next Section. ide on how to rphotos to itions. a of study is scale. (At ALS, dered at a scale h excellent should be close y to facilitate both airphoto llocated a number. dinates of the cene with the aid n a stable base, o factor so that basemap scale ting matrix of rol points for the in a map. ts per airphoto not only scale but three control compatibility g airphoto points cy between Landsat ntograph can points on the ng points on the the introduction of re to be preferred y O.M.I.) as they y adjust for pal points of ed to the basemap, c information s. at, highly rue to scale and orientation. The question now is how true this map really is. In the following Section the theoretical and empirical accuracy of map control by Landsat is discussed. 4.3 Theoretical accuracy ALS Landsat bulk processed photographic products are not portrayed with a particular map projection in mind. Apart from corrections for systematic influences (e.g. mirror velocity) ALS also corrects its images for panoramic distortion and earth curvature (Dovey, 1986). Whatever the along-line correction procedure may be, the portrayal result can only be related to an oblique cylindrical projection with as reference line the ground track of the satellite. Since the maximum distance away from this line in an MSS scene is only some ninety km, the theoretical distortion cannot amount to very much. As a result, ALS's bulk processed imagery indeed provides high planimetric accuracy over large areas as will be shown in Section 4.4. However, in bulk processing no account is taken of the direction in which Landsat is pointing during image acquisition. It is simply assumed that the satellite is pointing straight down, and scanning at right angles to its own path. To obtain higher accuracy than in bulk processed imagery it is necessary to employ ground control points with precisely known latitudes and longitudes. This permits a yaw-pitch-roll correction to be applied so that Landsat scenes can be produced with a higher planimetric accuracy (Dovey, 1983). Unfortunately, however, no precision products can be expected for the remote areas under discussion here, since in these areas points with known latitude/longitude are hard to come by. Another activity which influences accuracy is the pinpointing of the photo points in the Landsat image. The precision with which this can be done is not limited to pixel size as the points can be located to within pixel boundaries by interpolation if the airphoto is used as guidance. An MSS blow-up to e.g. 1/50 000 scale, of course, does nothing to increase Landsat's inherent accuracy but it does increase the accuracy of the cartographer who has to locate those points within the pixels. It should be remarked here that Landsat's spatial resolution, contrary to popular opinion, is not so much a function of the pixel size, but rather an expression of the variation in the spatial information content overlain and 'blurred' by the pixel grid. Thus defined, Landsat's spatial resolution is much finer than would be suggested by its pixel dimensions. Though it is unfeasible to quantify the method's accuracy on the basis of the above information, it has been possible, during the last few years in Irian Jaya, to assess its degree of magnitude thanks to 1 m accuracy measurements by the topographical teams. 4.4 Empirical accuracy In Irian Jaya Euroconsult was in a position to test a number of times the accuracy of the method under true field conditions. For six different areas ranging in size between 40 000 and 80 000 ha basemaps depicting the drainage network were produced using the Landsat map control method. The team also prepared a planimetric map in UTM projection for each area, showing traverses and secondary levelling lines (parallel to each other with 1 km spacing), along which all encountered river and stream intersections were indicated. The Landsat controlled basemap and the UTM planimetric map, both at the same scale, could now be matched by fitting river crossing to the drainage lines. As in this case the drainage pattern is a random one, it follows that the intersection pattern with parallel lines, is also random. It is remarkable that this random field of intersection points fits with the drainage pattern of the basemap as well as it does. The few mismatches invariably proved to be caused by mislocations of small streams on the air photographs. The method of best possible fit, used to mate intersections with streams, showed that the mean deviation which occurred was around 1.5 mm (when compensated for perpendicular intersection) in random direction, at a scale of 1/20 000. As ALS uses a process of portrayal which cannot be defined by a particular set of mathematical formulae, but which resembles the method as mathematically described for an oblique Mercator projection, and as the topographical team's results are displayed with the assistance of the UTM projection, a slight systematic mismatch caused by this difference of portrayal is to be expected. However, the absence of visible signs of systematic variation proves that for our practical purposes this mismatch is insignificant relative to the position variation caused by Landsat's geometric inaccuracies and with the uncertainties in the positioning of the control points in the Landsat image. Two other facts become apparent: * Without topographical work as a back-up, the method is adequate for the production of geographic maps with an accuracy requirement of 30 m, and * the photo interpreter can always, irrespective of tilt and scale variations, reconstruct the location of his field data on the airphoto, thus optimizing the quality of the interpretation. 5 DISCUSSION 5.1 Comparison It is possible to express the mean error as a function of control density in a slotted templet block. Conversely, knowing the mean deviation (1.5 mm at photo scale) in the airphoto map control method with Landsat, it is also possible to deduce the control density that would have been necessary had the slotted templet method been used. Of course, this comparison is only valid if photo tilts and scale variation are within ordinary limits, which as we know is not the case. Trorey (1947) has proved that the relationship is based on the theory of errors, from which it follows that the mean variation of image point locations is inversely related to the square root of the number of control points to which the slotted templet block is laid. Or e = kit/c)^ where e is the mean variation in mm, k a constant, t the number of templets, and c the number of control points. From empirical data Trorey determined the value of the constant k as 0.16. The theoretic control density (t/c) can now be calculated since e=1.5 and k=0.l6. It would seem that the 1.5 mm mean variation is comparable with the theoretical accuracy which would have been achieved with a control density of about 85 templets per ground control point had the slotted templet been used, and had airphotos been used with scale and tilt within acceptable limits. To achieve a result comparable to that of the Landsat airphoto map control method when using a set of photographs like those made available in southern Irian Jaya, the slotted templet method

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