1. Estimation of vertical forest structure and above ground biomass using ICESat/GLAS data
PADMA ALEKHYA V V L, SURAJ REDDY R, RAJASHEKAR G & JHA C S
Forestry and Ecology Group, National Remote Sensing Centre (ISRO), Hyderabad.
ABSTRACT
Ice, Cloud and Land Elevation Satellite (ICESat) - Geoscience Laser Altimeter System (GLAS) launched in January 2003 is the first space borne full waveform LiDAR sensor. The LiDAR waveform is used to estimate the forest canopy height using waveform derived parameters extracted using signal decomposition techniques. In the present study, we estimated average tree canopy heights and AGB from GLAS waveform parameters by using a multi-regression linear model across different forest types in Madhya Pradesh, India. The ICESat-GLAS derived heights were correlated with field measured tree canopy heights for 60 plots. Results have shown a significant correlation of R2= 74% for top canopy heights and R2= 57% for stand biomass.
INTRODUCTION
Space-borne LiDAR data has been used to generate global and regional maps of tree heights and forest biomass
ICESat/GLAS is a waveform sampling LiDAR which emits for a short duration (5 ns) laser pulses towards land surface and records the returned echo.
Objectives of GLAS instrument include:
Sea-seasonal changes in ice sheet elevations
Measurements of cloud and aerosol height profiles
Vegetation canopy heights
GLAS consists of three lasers operating at 1064 nm wavelength for surface and cloud top measurements and records the returned laser energy from an ellipsoidal footprint
ICESat offers 15 GLAS products (GLA01 to GLA15) out of which GLA01 and GLA14 are used for our study
GLA01 (L1A Global Altimetry Data Product) provide the waveforms for each laser shot, For the land surfaces, the waveform has 1000 bins with a bin size of 1-nsec or 15cm or 0.15m, attributing to the total waveform length of about 150m.
GLA14 is L2 Global Land Surface Altimetry product and it contains precise geo-location along with elevation of the footprint center
Lorey's mean height (hz) describes the mean height weighted by basal area of corresponding trees.
Where g is the basal area of individual tree in the plot, h is the height of corresponding tree in each plot.
Study Area Showing the GLAS Footprint Tracks across Madhya Pradesh.
Waveform parameter Extraction
(Waveform Start signal, End signal, Waveform centroid, Waveform Extent, Waveform distance, Peak distance, HOME, No. of Gaussian fits, H25, H50, H75, R25, R50, R75, Top Canopy Height)
Waveform Processing/ Normalization & Gaussian Fitting
Geolocated Footprint over Study area
Counts to Volts Conversion
Exported as ASCII
Linked using unique Record Number and Shot Number
Decomposed Waveform
GLAS DATA
GLA 01
(Rec_num,
Shot time,
Waveform information)
GLA 14
Date, time,
Lat,Long,
Shot time)
(32m X 32m) in GLAS footprints
Sample field plots
GLAS raw waveform with different Gaussian fits
Prediction of top tree height and stand biomass from GLAS data
CONCLUSION
Evaluate the potential of ICESat/GLAS to estimate canopy height and above ground biomass in the forests of Madhya Pradesh, India.
Canopy height was estimated from GLAS products explained about 74% of the variance in comparison with the field measurements.
57% of variability in field measured AGB using GLAS derived parameters.
Future work will focus on increase in field plots to areas of tall trees and to extend the relations to regional and national level studies.
Generation of forest height map for spatial biomass estimate through data mining approaches.
Multi-regression linear model parameters for estimation of Lorey's height and Above Ground Biomass (AGB)
Parameter
Intercept
HOME
H25
H75 R2
F - Statistic
(p<0.01)
Lorey's Height (m)
1.214
-0.204
0.117
1.018
0.741
53.4
AGB
(T ha-1)
4.413
-7.996
6.532
8.960
0.572
25.4
REFERENCES
Lefsky, M. A., D. J. Harding, M. Keller, W. B. Cohen, C. C. Carabajal, F. D. B. Espirito-Santo, M. O. Hunter & R. de Oliveira Estimates of forest canopy height and aboveground biomass using ICESat. Geophysical Research Letters 32: L22S02.
Lefsky, M. A A global forest canopy height map from the Moderate Resolution Imaging Spectroradiometer and the Geoscience Laser Altimeter System. Geophysical Research Letters 37: L15401.
Duong, H. V Processing and application of ICESat large footprint full waveform laser range data. Doctor thesis of the Delft University of Technology, Netherlands.