We use passive optical high-resolution GeoEye-1 imagery and active synthetic aperture radar (SAR) Advanced Land Observing Satellite (ALOS-1) phased array type L-band synthetic aperture radar (PALSAR) L-band horizontal–horizontal-polarization imagery to estimate forest aboveground biomass (AGB) of the tropical mountainous forest test site in Kayar Khola watershed, Chitwan district, Nepal. Object-based tools were used to delineate tree crowns from the orthorectified pan-sharpened GeoEye-1 optical imagery. AGB modeling with crown projection area extracted from the optical imagery shows a good linear relationship with R2=0.76. The terrain-corrected, radiometrically calibrated, and speckle-filtered ALOS-1 PALSAR backscatter image was utilized for AGB modeling; the nonlinear modeling of AGB with the SAR backscatter (dB) shows R2=0.52. The validation R2 values for AGB estimates from GeoEye-1 and ALOS-1 PALSAR are 0.83 and 0.44, respectively. The direct comparison of AGB estimates from both sensors is made possible by the utilization of the same set of ground survey points for both training and validation of the statistical models for both datasets. The final AGB output maps from both sensors show that the spatial patterns of AGB are in reasonable agreement at lower elevation, while SAR seems to underestimate AGB values as compared with optical-based estimates in the higher elevation zones.
This paper provides novel analysis of existing interpolation techniques and suggests improvement for more
accurate orthorectification of satellite imagery. Traditional methods for measuring geo-location use Ground
Control Points (GCPs). The accuracy of these methods depends on the accuracy of GCPs. The accuracy of geolocations
can also be improved by using Digital Elevation Model (DEM) which incorporates topographic relief
displacement to measure geographic locations. Since the accuracy of geographic locations is dependent on the
resolution of DEM, in our study, the accuracy of geo-locations was assessed using interpolated DEMs of multiple
resolutions. The comparative analysis showed that the accuracy of geo-locations can be improved by increasing
the resolution of DEM using interpolation.