Study On Orthophoto-forest Map Making And Forest Measurement Based On Aeroscape

Forestry map-making and forest measurement are main tasks using airscapes in forest resource survey .according to the theory of self-calibrating bundle aerotriangulation .Using OrthoBASE module of ERDAS software, 176 digital airscapes consisted of 13 strips were orthorectified differentially finally , orthophoto - forest map and traditional forest map which only have 2.953 meter RMS was made firstly including total maoershan forest farm map of 1:25000 and every forest region map of 1:10000 in forestry department of China. Image displacement caused by camera tilt and terrain fluctuation is eliminated or reduced greatly. And image errors mainly caused by camera lens distortion, photographic material deformation, atmospheric refraction and earth's curvature are eliminated or reduced greatly. Finally, using Janlagou forest region as example, forest measurement of area, crown closure, forest stand mean height and individual standing tree height is studied by means of map include digital orthomage and forest map , elements of exterior orientation and Digital Surface Model. Main tasks have been finished in this paper, as follows:Firstly , according to the control point distribution plan , 91 image control points include X,Y and Z coordinates (all are Fixed) were measured adopting RTK measurement technology of GPS. Total 95 image control points are gained adding 4 control points which are purchased from survery and mapping department, the control point maximum error is decimeter.Secondly , four relief maps with the scale of 1:50000 were scanned by 600 dpi and rectified by three order polynomial , coordinate accuracy of every map is as follows: X coordinate error root-mean-square (ab, RMS) is 0.0036 pixel , Y coordinate error RMS is 0.0014 pixel , total error RMS of X and Y is 0.0038pixel in No.l relief map; X coordinate error RMS is 0.0042 pixel , Y coordinate error RMS is 0.0020 pixel , total error RMS of X and Y is 0.0047pixel in No.2 relief map; X coordinate error RMS is 0.0043 pixel , Y coordinate error RMS is 0.0022 pixel , total error RMS of X and Y is 0.0048pixel in No.3 relief map; and X coordinate error RMS is 0.0026 pixel , Y coordinate error RMS is 0.0007 pixel , total error RMS of X and Y is 0.0027pixel in No.4 relief map. Finally , mosaic relief map made of four relief maps accuracy is verified , and the results are showed : in the six check points , X coordinate maximum error (â–³X ) is 1.741meter , minimum 0.737 meter and average 1.119 meter; Y coordinate maximum error (â–³Y) is 1.501meter , minimum 0.515 meter and average 1.006 meter ;the maximum error is 2.026, and the minimum error is 0.517meter in the total error RMS (T_i )of a single check point; the six check point total error RMS (T) is 1.749meter.Thirdly , DEM with 5 meter resolution was made respectively by triangle linear interpolation and triangle nonlinear interpolation .and the accuracy of two DEMs was verified using the method of check point and method of contour line recreation and sampling . Total 49 check points were checked in the method of check point , and the results show that the total error RMS of linear interpolation is 4.1meter , and the total error RMS of nonlinear interpolation is 3.8 meter , accuracy of nonlinear interpolation is slightly higher than linear interpolation . contour lines in Total18 grids of kilometre were sampled and compared with original contour lines , and the results show that degree of coincidence is 96% for linear interpolation , and 96.5% for nonlinear interpolation .accuracy of nonlinear interpolation is slightly higher than accuracy of linear interpolation.Fourthly, A method of absolute and relative position is put forward to calculate the original values of exterior elements , it solved the problem of exterior elements original value in self-calibrating bundle aerotriangulation.Fifthly f According to the theory of self-calibrating bundle aerotriangulation , exterior orientation elements of every airscape , original GCPs and tic points were calculated . the differences between original GCPs and calculated GCPs were computed and showed that the maximum X coordinate error was 4.604 meter , total X coordinate errors RMS were 1.449 meter ; the maximum Y coordinate error was 4.833 meter , total Y coordinate errors RMS were 1.528 meter; the maximum Z coordinate error was 4.244 meter ? total Z coordinate errors RMS were 2.052 meter. So we can think that the accuracy is much higher, because 1 mm in orthophoto means 10 meter on the ground for the orthophoto with the scale of 1:10, 000 , this fact show that the GCPs error in the orthophoto is less than lmm. tic points maximum x image coordinate error is 0.0152 pixel , and maximum y image coordinate is 0.0144 pixel the accuracy is much higher.Sixthly , Three methods of forest map making from ploted areoscapes to stand map are put forward throgh working experiences.Seventhly, Many factors of compartment and subcompartment in forest map are marked automatically by means of secondary development function of AutoCAD software.and productivity of forest map making is improved greatly.Eighthly, comparing area measurement error of orthorectified airscape and unorthorectified airscape in three kinds of terrain. The results show that measurement error of flat ground is lowest , that is 1.2%; 3.3% is in middle and low mountain area , and 11.5% is the most biggest measurement error in high mountain area. These show that area measurement error is much higher in the unorthorectified airscape , we should overlook it . and counting up the forest survery results of Maoershan mountain forest farm in 2004.Ninthly, using the methods of unsupervised classification and recoding to calculate degree of closing are put forward , this paper get much better results which show that the calculation vaule is the same as measurement vaule in No.l sample area , and the difference between calculation value and measurement value is only 0.1.Tenthly, Using Digital Vegetation Height Model (ab.DVHM) made of the difference between Digital Surfacing Model(ab.DSM) and Digital Elevation Model (ab.DEM) to measure stand mean height is put forward firstly in this paper. DVHM can reflect totally vegetation height distribution , and to a certain degree .reflect stand age-class distribution .measuring average height of every subcompartment in Janlagou forest region by means of DVHM.Finally, according to the theory of bundle aerotriangulation, using exterior orientation elements to calculate the elevation of crown top and root of tree is put forward firstly .this paperconducts the experiment on tree measurement , the results show that error can be less than 2 meter by comparing measurement tree height with computation tree height. Stereoscope is not used to measure trees in the method.