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Data use cases

Methodology | Results

Note that, at this date (late 2010), Cryosat data are still preliminary and will be re-processed and completed at a later date, in particular with mean surfaces and such.

Data used

Low Resolution mode data
The low resolution mode data are the data from the time Cryosat is in the most classical (pulse-limited) altimeter mode. This mode is generally active wherever no margins are expected (outside some test areas), i.e. on ocean and in the interior of interior of iced lands, including Greenland and Antarctica.

SAR and SAR-In mode
SAR mode enables to increase along-track resolution, and thus be able to capture more abrupt height variations (including the ones due to sea ice). Note that this is not an imagery mode as the SAR data may be.
SAR-interferometric enables to retrieve slope value where the measurements were taken. It is mainly used over ice caps margins/glaciers

We will look at waveform data in SAR and LRM mode (L1b data)

See Cryosat pages on this site for more information
Data can be obtained from EOHelp

Methodology

We will use the Basic Radar Altimetry Toolbox to have a look on waveform shapes over Arctic with the SAR mode data and over ocean with SAR and LRM modes - for comparison purposes.

Geographical / Temporal extraction

We will use one file over Artic, one over Atlantic, off the Portugal coasts (SAR mode) and one over the Atlantic (LRM mode). Note that Cryosat L1b data are not provided by tracks or half-orbits, since the mode may change (L2 "GDR" data are, however, with a flag to indicate the mode).

• CS_OFFL_SIR_LRM_1B_20101111T084452_20101111T085219_A001.DBL (LRM mode data, taken on 2010/11/11,in the Atlantic)
• CS_OFFL_SIR_SAR_1B_20101111T001539_20101111T002242_A001.DBL (SAR mode data, taken on 2010/11/11,in the Arctic)
• CS_OFFL_SIR_SAR_1B_20101111T195241_20101111T195604_A001.DBL (SAR mode data, taken on 2010/11/11,off the coast of Portugal)

Operations

In the "Datasets" tab, we select the three files, each in a different dataset.

In the "Operations" tab, create four operations as follows: one using LRM mode data, one SAR mode data off the coast of Portugal and two using SAR mode data in the Arctic.
For all four operations, select the latitude that is in the for "X" within the "time_orb_data" record (in order to have high-resolution latitude), and as "Data expression", the field "avg_pow_echo_wavef" (in the "wavef_data" record), which contains the 128 Ku-band waveform samples for each waveform.

In the "Selection criteria" expression, the geographical boundaries are limited as follows for the SAR mode data in the Arctic (CS_OFFL_SIR_SAR_1B_20101111T001539_20101111T002242_A001.DBL):
- is_bounded(-180, lon, -90) (for the first part of the track)
- is_bounded(110, lon, 180) (for the second part of the track)
this is needed in order to see the waveforms vs latitude in a chronological sequence (since the satellite goes from (-90°E, 82°N) to (110°E, 72°N) through 88°N. Otherwise, you can put in "mdsr_time" as X, but you won't be able to localize immediately your waveforms with the plot.
Execute the Operations

In the "View" tabs, you can choose between two different kind of graphs:

• Y=F(X) which plots the waveforms individually and represents the return echo power in function of time every 1/20th of a second.
• Z=F(X,Y) which plots a set of cumulated waveforms in function of latitude, as if seen from above.

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Tutorial produced by CLS under contract to ESA and CNES