# base2freeboard documentation

base2freeboard is part of Antarctic Mapping Tools for Matlab (Greene et al., 2017). Click here for a complete list of functions in AMT.

base2freeboard estimates freeboard height above sea level, from ice basal elevation, assuming hyrostatic equilibrium.

## Syntax

```F = base2freeboard(T)
F = base2freeboard(...,'rhoi',iceDensity)
F = base2freeboard(...,'rhow',waterDensity)
F = base2freeboard(...,'rhos',snowDensity)
F = base2freeboard(...,'Ts',snowThickness)```

## Description

F = base2freeboard(T) estimatesfreeboard height height above sea level F in meters above the geoid from ice thickness T in meters.

F = base2freeboard(...,'rhoi',iceDensity) speccifies ice density in kg/m^3. Default ice density is 917 kg/m^3.

F = base2freeboard(...,'rhow',waterDensity) specifies water density in kg/m^3. Default water density is 1027 kg/m^3.

F = base2freeboard(...,'rhos',snowDensity) specifies snow density in kg/m^3. Default snow density is 350 kg/m^3, however the default snow thickness is 0 m, so the snow density value will only affect calculations if snow thickness is specified.

F = base2freeboard(...,'Ts',snowThickness) specifies snow thickness in meters. Default snow thickness is 0 m.

## Example 1:

An iceberg's base is 4.5 m below sea level and it's made of pure ice. How high is the iceberg's surface above sea level?

```F = base2freeboard(-4.5)
```
```F =
0.54
```

## Example 2:

Imagine this elevation profile measured by a laser altimeter:

```x = 0:1000;

% A random profile:
z = movmean(randn(size(x)),75);
z(z<0) = 0;

plot(x,z,'r.')
xlabel 'distance along profile'
ylabel 'elevation (m)'
box off
``` Where's the ice base? It's the surface minus the thickness:

```base = z - freeboard2thickness(z);

hold on

% Draw the ice:
patch([x,fliplr(x)],[base,fliplr(z)],'b','facecolor',rgb('ice blue'))

% Draw the water:
yl = ylim; % y limits of the axis
h = patch([xlim,fliplr(xlim)],[yl(1) yl(1) 0 0],'b',...
'facecolor',rgb('ocean blue'));
uistack(h,'bottom') % sends "water" to the back
``` ## Citing AMT

If this function or any other part of Antarctic Mapping Tools is useful for you, please cite the paper that describes AMT.

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 was written by Chad A. Greene of the University of Texas Institute for Geophysics (UTIG), April 2017, for inclusion in the Antarctic Mapping Tools package.