MATLAB Examples

# istidal documentation

The istidal function returns logical true for everything seaward of the landward limit of flexure (including open ocean and ice shelves) detected by InSAR according to MEaSURES Antarctic Boundaries for IPY 2007-2009 from Satellite Radar, Version 2. This is the same thing as the logical NOT of isgrounded.

The Antarctic Boundaries dataset is described on the NSIDC site here. An overview of the tools in this AMT plugin can be found here.

## Syntax

```tf = istidal(lati,loni)
tf = istidal(xi,yi)```

## Description

tf = istidal(lati,loni) returns true for all geo locations (lati,loni) not identified as grounded ice in the Mask_Antactica_v2.tif (sic) dataset.

tf = istidal(xi,yi) returns true for all locations not identified as grounded ice in Mask_Antactica_v2.tif (sic), where input coordinates are automatically determined to be polar stereographic (true lat 71 S) meters if their values exceed the normal lat,lon range.

## Example: Mask a gravity dataset:

This example uses a Gravity Plugin for AMT to load some example data, but I'll show you how you can follow along without loading that dataset. Whether you have the gravity plugin or not, begin by creating a 300 km wide grid centered on PIG, at 0.25 km resolution:

```[lat,lon] = psgrid('pine island glacier',300,0.25); ```

If you have the gravity plugin, interpolate gravity values to the grid like this:

```FA = gravity_interp(lat,lon,'free air'); ```

If you don't have the gravity plugin you can simply use random data like this:

`FA = rand(1201);`

Use istidal to find out which parts of the dataset are not over grounded ice:

```salty = istidal(lat,lon); ```

Mask-out all tidal ice (use the tilde for NOT) by setting it to NaN:

```FA(~salty) = NaN; ```

Note, the istidal function returns the logical NOT of the isgrounded function, so we alternatively could have done the above step like this:

```FA(isgrounded(lat,lon)) = NaN; ```

Plot the gravity data corresponding to wherever there's ocean water:

```pcolorps(lat,lon,FA) axis tight ```

For context, overlay a red grounding line and a black coastline:

```antbounds('gl','r') antbounds('coast','k') ```

## Citing this dataset

If you use this dataset, please cite the following:

• The dataset: Mouginot, J., B. Scheuchl, and E. Rignot. 2017. MEaSUREs Antarctic Boundaries for IPY 2007-2009 from Satellite Radar, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. http://dx.doi.org/10.5067/AXE4121732AD.
• Antarctic Mapping Tools: Greene, C. A., Gwyther, D. E., & Blankenship, D. D. Antarctic Mapping Tools for Matlab. Computers & Geosciences. 104 (2017) pp.151-157. doi:10.1016/j.cageo.2016.08.003.

## Author Info

This function and supporting documentation were written by Chad A. Greene of the University of Texas Institute for Geophysics (UTIG), November 2016. Updated May 2017.