5. ACCURACY ANALYSIS OF PRISM MEASUERD TREE
HEIGHT
5.1 Theoretical Accuracy Analysis
In the Study, photogrammetric measurement of forest plays veryimpor-
tant role. Especially, the accuracy of the tree height measurements is
the most critical technology for supporting forest carbon stock model
based on the upper tree height. A theoretical analysis of the tree height
measurement accuracy was first carried out. According to the researchs
(Uchida et al.,2008), the theoretical accuracy of planimetry and height
in measurement of stereo satellite images is generally
expressed as follows:
ox=0y=Hf x o, (1)
oz= HBXHf x o,
where ox, oy: Theoretical accuracy of planimetry
oz: Theoretical accuracy of elevation
o,; Measurement accuracy of image coordinates
The value of o, is generally 0.2 - 0.5 pixels, but can be 1 pixel
maximum. Here, value of g,= 0.5 pixel was assumed and 0.2.5 m.
52 Accuracy Analysis Comparing Tree Heights from
ALOS/PRISM Measurements and Forest Plot Survey
In order to verify the accuracy of tree height measurements, PRISM
measured tree heights and the forest survey data were compared at 16
plots. The results are as follows:
- Standard deviation of discrepancies (errors): oz. 39m
- Minimum discrepancy: 02m
- Maximum discrepancy: 64m
- Mean PRISM measured tree height: 20.2 m
- Mean field measured tree height: 20.1 m
- Difference of the mean values: 0.1 m
These values were very similar to the result of the previous study in
Vietnam.
5.3 Accuracy Analysis using PRISM Images Before and After
Forest Cutting.
In order to verify the accuracy of PRISM tree height measurements at
estimated ground height, 146 locations showing conditions before- and
after-forest-cutting were selected from ALOS/PRISM images acquired
over LPB province in November 2007 and January 2010. Then, the
estimated ground height and the height of the ground that can be
visually confirmed at same location were measured on the before- and
after-forest-cutting PRISM stereo images using a digital stereo plotter.
The ground elevations measured on two PRISM images were
compared to estimate accuracy of the estimated ground heights. As a
results of verification at 146 selected points, the amount of
discrepancies was oz,=4.4 m (standard deviation) ranging from 0.0 m
to 11.6 m. Furthermore, the measurement accuracy of PRISM
measured tree heights oz can be estimated trough applying the error
propagation principle:
Om -SQRI(Z + Oz, ) zsim 2)
where the theoretical error is assumed to be 0.5 pixel.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
Various parameters affecting the accuracy of the PRISM measured tree
height were examined. And, it was shown that the most important
factor is slope of terrain and associated sun light illumination (aspect).
From these results, it can be said that it is necessary to measure tree
height with special care when the slope is steep.
6. SUMMARY
Some results of the case study on MRV system for REDD+ in Lao
PDR and improved methods for reducing difficulty of forst surveys at
isolated areas and for estimating forest carbon stock using biomass
classing were reported in this paper. The results of accuracy analyses of
tree height measurement utilizing ALOS/PRISM showed that the error
of the mean value of many measurements is reasonably well even
though the errors of individual observtions are relatively large. From
the results of the Study, the tree height data from sreteo satellite images
can be used as at least effective additional data for forest carbon stock
estimation based on ordinary forest surveys on the ground. The same
thing can be said to the forest biomass classing data. The scope of
MRV in the REDD+ mechanism is broad and complex as forests
themselves are. It is very important to do some traial studies before
establishing an actual MRV system in practice as shown in this paper
since it is needed to establish a sustainable MRV system for REDD+.
Acknowledgements:
Authors would like to express sincere gratitude for the supports,
cooperation and advices offered by the Forest Agency, Ministry of
Agriculture, Forestry and Fishery, Japan, the Department of Forestry
and Forest Inventory and Planning Division (FIPD), Ministry of
Agriculture and Forestry, Lao PDR, and the Advisory Committee
(Chaired by Dr. Haruo SAWADA, Professor of the University of
Tokyo) in the Study.
References:
l. Asia Air Survey Co., Ltd.2011. Progress Report of the Study on
the Strengthening of Methodological and Technological Approaches
for Reducing Deforestation and Forest Degradation within the REDD
Implementation Framework, http://www.ffpri.affrc.go.jp/redd-rdc/ja/
reference/list-02.html.
2. GOFC-GOLD,2010. Sourcebook of methods and procedures for
monitoring and reporting anthropogenic greenhouse gas emissions and
removals caused by deforestation, gains and losses of carbon stocks in
forest remaining forests, and reforestation COP17 version 1.
3. IPCC, 2006. IPCC Guidelines for National Greenhouse Gas
Inventories, http:/www.ipcc-nggip.iges.or.jp/public/2006gl/index html.
4. IPCC,2003. GPG-LULUCF (Good Practice Guidance for Land
Use, Land-Use Chang and Forestry), http://www.ipcc-nggip.iges.orjp/
public/epglulucf/epglulucf contents.html.
5. Kamusoko, Courage et al.,2011. Spatial Simulation Modelling of
Future Forest Cover Change Scenarios in Luangprabang Province, Lao
PDR, Forests 2011, 2(3), http;/www.mdpi.com/1999-4907/2/3/107/.
6. Uchida,S.,2008. Evaluation about the precision on the figure of the
medium- and high-levels resolution satellite image, 2008 photographic
surveying society memoir, Japan.
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