GLAH06 — Land Ice Elevation¶

GLAH06 provides 40 Hz ice sheet elevation data from the Geoscience Laser Altimeter System (GLAS) instrument on ICESat.

Quick Start¶

using SpaceLiDAR, DataFrames

g = granule("GLAH06_634_2131_002_0084_4_01_0001.H5")
t = table(g)
df = DataFrame(t)

Default Columns¶

Column	HDF5 Path	Type
`longitude`	`Data_40HZ/Geolocation/d_lon`	Float64
`latitude`	`Data_40HZ/Geolocation/d_lat`	Float64
`height`	`Data_40HZ/Elevation_Surfaces/d_elev`	Float64
`datetime`	`Data_40HZ/DS_UTCTime_40`	DateTime
`saturation_correction`	`Data_40HZ/Elevation_Corrections/d_satElevCorr`	Float64
`elev_use_flg`	`Data_40HZ/Quality/elev_use_flg`	Int8
`sigma_att_flg`	`Data_40HZ/Quality/sigma_att_flg`	Int8
`i_numPk`	`Data_40HZ/Waveform/i_numPk`	Int32
`height_reference`	`Data_40HZ/Geophysical/d_DEM_elv`	Float64

Coordinate System¶

TOPEX/Poseidon ellipsoid

ICESat data uses the TOPEX/Poseidon ellipsoid, NOT WGS84. Call topex_to_wgs84!(df) to convert heights to WGS84.

Heights must be corrected for saturation before reprojection:

t = table(g)
df = DataFrame(t)
dropmissing!(df, :height)
icesat_saturation_correct!(df)  # height += saturation_correction
topex_to_wgs84!(df)             # reproject to WGS84

Quality Flag¶

The quality flag from Smith et al. (2020) combines multiple criteria:

q = icesat_quality(df)
# Equivalent to:
# (elev_use_flg == "valid") & (sigma_att_flg == "good") & (i_numPk == 1) & (saturation_correction < 3)