Fortran 95 and C++ tools for the processing and analysis of ICESat data, in particular for extracting Antarctic megadunes parameters.
Algorithms created in collaboration with Debbie Biscaro and Maja Radivojevic (Museo Nazionale dell'Antartide, Siena, Italy).
Currently only Fortran algorithms are here described.
ReadGLA12: reads a set of input GLA12 files, stored in rel. 34 format (the current one as of 2016-04-30).
HeightVarGla: calculates height differences between elevation pairs within a user-defined search radius.
ElevationDecimation: filters elevation data (point) based on a user-defined grid size, producing a subset of original poit data. See [post] (https://gisoftw.blogspot.it/2010/09/too-many-elevations.html)
MegaduneAmplitude: derives the amplitudes of megadunes
MegaduneMinMax: derives the locatiion of minimum and maximum elevations along elevation tracks.
MegaduneParameters: calculates descriptive parameters of megadunes
SlopeRatio: calculates the ratios between upward- and dwonward facing slopes
MegaduneWavelength: calculates the wavelengths of megadunes.
Since data in GLA12 files are in big-endian notation (the Unix default), when working in Windows you must compile the program using the big-endian data option. For instance, with the free g95 compiler, the command line should include the "-fendian=BIG" option, e.g.:
> g95 ReadGLA12_v5.0.f95 -fendian=BIG -o readgla12.exe
> g95 HeightVarGLA_v1.0.f95 -fendian=BIG -o heightvar.exe
This Fortran console program reads data from a set of binary ICESat files, filters them according to user defined geographic, temporal and quality settings and writes the resulting records into both ascii files, for GIS import as point layers, and also a binary file, to be used with the "HeightVarGLA" program for the detection of height differences between neighbouring elevations).
The original version of the algorithm is described in Alberti & Biscaro (2010).
The program input is constituted by a set of GLA12 files, plus a pair of text files, a former listing the GLA12 files to analyse and a latter a set of analysis parameters. All this files ahve to be stored in a single directory reachable by the program (for instance change the working directory to this directory before running the exe file)
The list of GLA12 binary files to read is composed by one record for line, e.g.:
GLA12_03022021_r2973_428_L1A.P1387_01_00 GLA12_03092517_r2973_428_L2A.P1387_01_00 GLA12_03100413_r2973_428_L2A.P1387_01_00 GLA12_04021721_r2973_428_L2B.P1387_01_00 GLA12_04051816_r2973_428_L2C.P1387_01_00 GLA12_04100321_r2973_428_L3A.P1387_01_00 GLA12_05021715_r2973_428_L3B.P1387_01_00 GLA12_05052016_r2973_428_L3C.P1387_01_00
......
An example of parameters is:
-90 90
-180 180
2005 1 1 2009 1 1
300 100
where:
-90 90 # minimum and maxixum latitude
-180 180 # minimum and maxixum longitude
2005 1 1 2009 1 1 # time window: initial and final year month day; if not required: -1 as first value
300 100 # filters on saturation elevation correction and gain value; when not desired substitute value with -1 (e.g. 300 -1 or -1 100 or -1 -1 )
The output consists of a set of ascii files for GIS import, each one corresponding to an input Glas binary file, and a binary file for height variation analysis with the HeightVarGLA program.
You can find further methodology details in Alberti & Biscaro (2010).
This algorithm calculates height differences between elevation pairs within a user-defined search radius. Suggested values are between 50 and 500-1 000 m, depending on the desired output resolution and on the slope and roughness of the topographic surfaces.
The user can choose to output results only within a predefined range of the elevation differences, e.g., all pairs with height differences between 0.5 m and 5 m.
More details are in Alberti & Biscaro (2010).
The input for the elaborations consists of one or two binary files (with .dat extension) created by the ReadGLA12 program, storing data for a specific geographic domain acquired in a single time interval (when using one input file) or in two different time intervals (two input files).
Filtered-in pairs are written in an output text file that can be easily imported into GIS software. A metadata file stores information about the analysis session and analysed tracks (e.g., time, input files, used thresholds on distance and elevation differences, and summary results for each track).
Alberti, M., Biscaro, D., 2010. Height variation detection in polar regions from ICESat satellite altimetry. Computers & Geosciences 36, 1-9.
GLA 12 Records: Release 34 at http://nsidc.org/data/docs/daac/glas_altimetry/gla12_records_r34.html