Vegetation
Canopy Lidar (VCL)
-Calibration\Validation-
Vegetation
Canopy Lidar (VCL)
The VCL science team has primary responsibility for calibration of algorithms for extracting geophysical fields, for validation of the results, and for assuring the accuracy and quality of the science data products. These calibration/validation activities include calibration of surface height (range) measurements, calibrations relating laser returns to some measure of canopy top height, and validation of VCL data products.
Calibrating surface height measurements.
Calibration of ground height measurements requires both instrument
and attitude on-orbit bias and drift retrievals. Several techniques will
be utilized to obtain these data including: comparisons of VCL ocean altimetry
with sea surface observed and derived from suitable ocean radar altimetry
missions such as TOPEX/Poseidon, comparisons with precisely known land
topography, and application of laser altimeter dynamic crossovers.
Calibrating canopy top heights.
The science team are developing an unambiguous calibration relating
the VCL canopy measurment and the most widely encountered definition of
stand height. To help with this calibration we have acquired aircraft data
with the Laser Vegetation Imaging Sensor (LVIS) instrument (Blair et al.
1998), configured as a VCL simulator over a variety of forest types including
moist tropical forests, deciduous and mixed conifer, and open woodland,
among others.
Validation.
Validation has three components: comparing results from aircraft data
with localized ground data, comparing VCL data products with aricraft data
for the same areas, and comparing gridded products with data from global
site networks. The combination allows us to scale from small field plot
data to landscape-level estimates, an then to gridded products from VCL.
Alogrithms for Level 2 products are validated by comparison with ground
data. Level 1 and Level 3 products are validated by comparing them with
aircraft data and landscape estimates from aircraft data respectively.
Global Level 3 products are checked against several distributed data sources.
Validation exercises for the VCL project are ongoing.
Data have been collected for: