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Poster Session
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An approach for estimating forest stock volume by using space Remote Sensing data
Results and Analysis
- Four groups of equations from four different base variable were obtained in accordance with the above described ways of sample plot design and selection. The results demonstracted no significant difference for the various ways of sample selection.
The county comprises mainly two drainage areas of Pu river and Luan River, To make the estimate equations tally properly with the actual situation, they were calculated separately in accordance with the two major river systems. The correlation coefficients were obviously raised after the two major drainage areas had neen treated separately, and the estimates thus achieved represented properly the distribution of stock volume.
At the same time, the effects of stock volume estimation by merely using density values were compared with that of stock volume estimation by addition of the ratio terms. The comple x correlation coefficient for the regression equations established between stock volume and density values of TM bands 1,2,3,4 was only 0.4818, however, after the addition of ratios 4/3 and (4-3)/(4+3), the complex correlation coefficient increased to 0.7262, which indicated the important influence of the ratio terms. When the qualitative factors were added, an approximate deter mination of the boundary lines between forest and non-forests could be made, though the estimation precision was not further improved.
- Tanking the group angle gauge measurement as an example, there are two kinds of methods to compute the stock volume for the whole county:
- The stock volume of forested land (19,72, M3/ha.) was multiplied by the total area of the county (329,832 ha.) and then by the coverage (30.65%), and the total stack volume of the county (1,993, 557.934 M3) was obtained.
Table 1 comparision of the sesults actually measured of Ping Quan county with those estimated by various mehtods (figures were of relative errors)
| Methods |
size/form
of plots |
choice of
plots |
compared vith
non-strtified
Sampling |
compared with
stratified
butnon-mappd smplng |
Note |
Multivar
Regress.
Estimate |
Angle gauge
0.02 /sq. |
Group-av.
Group-av. |
+2.6
+17.7 |
-10.7
+1.8 |
|
Stratif.
2-stage
sampling |
|
0.01
0.01 |
-4.4
14.4 |
-8.0
-14.9 |
3 selected from
5 plots per group |
0.02/sq.
angle gauge |
Centeral
Centeral |
+18.8
+5.4 |
+15.2
+1.7 |
Sampling according
To Air photos |
Double
Sampling
Estimation |
angle gauge
0.01/sq |
Centeral
Group-av. |
+22.88
-11.73 |
+10.6
-24.6 |
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- The stock volume estimates of all the points (including the points actually measured and those interpreted) were substituted for with the regression equation, and the general average of stock volume for the whole county was computed (6.9475 m3/ha.). The total stock volume of the whole county was estimated to be 2,291,500 M3) in this method. The two methods had 6.9% difference, and the second method of calculation seems to be more reasonable.
It can be seen from Table 1 that the accuracy of various procedures usually reaches 80%. Each procedure has its different advantages and applicability: the double sampling procedure with air photos and ground plots (method 3) can increase estimation precision by doing an amount of indoor work but limited field check, while the two-stage sampling procedure by combining satellite data and aerial photographic data can increse work efficiency. The direct application, however, of satellite images in estimation of stock volume is a new test and experiment. It is worth of notation that the combined procedure of qualitative and quantitative facotrs proves to be simple and convenient, and easy to spread It can also satisfy the precision requirements.
References
- Strahler, A.H., timber inventory using LANSAT, The Eighth Candian symposium on Remote Sensing, pp 665-673.
- Tang S.Z., Xu G. H., A Study on the method of estimation of forest stock volume by LANDSAT digital image data-principle and Method, Remote Sensing Research and Application Materials, Science and Technology Document Press, pp 142-147, 1984.
- Zhao X. W., A preliminary study of the estimation of forest distribution and stock volume by directly using satellite images, Gaungdong Forest Newslatter, (2); 18-20, 1894.
- Dong W.q.etal. quantitativeapproachesandtheir application, Jiling Peoples' Press, 22, 1979
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