The itslive_data function reads ITS_LIVE mosaic data into MATLAB.
Z = itslive_data(region, variable)
Z = itslive_data(..., xlim=xlim, ylim=ylim)
Z = itslive_data(..., latlim=latlim, lonlim=lonlim)
Z = itslive_data(..., buffer=buffer_km)
Z = itslive_data(..., year=years)
Z = itslive_data(..., filepath=path)
[Z,x,y] = itslive_data(...)
[Z,Lat,Lon] = itslive_data(...,geoout=true)Z = itslive_data(region, variable) loads any gridded variable in the ITS_LIVE v2 summary velocity mosaics for a specified region. The region is a number between 1 (Alaska) and 19 (Antarctica). To view a map of the regions, type itslive_regions. By default, the climatology mosaics are plotted. The input variable can be "v", "vx", "v_error", etc.
Z = itslive_data(..., xlim=xlim, ylim=ylim) only loads data within specified map limits. With this syntax, xlim and ylim can be two-element arrays indicating the minimum and maximum spatial extents of interest, or you can enter many scattered points and the function will automatically calculate the minimum and maximum values of the x and y limits.
Z = itslive_data(..., latlim=latlim, lonlim=lonlim) similar to the xlim, ylim above, but here geo coordinates are entered. 1
Z = itslive_data(..., buffer=buffer_km) adds an extra buffer around the limits specified by xlim,ylim or latlim,lonlim. The input buffer_km can be a scalar value to add a specified buffer on all sides of the input points, or can be a two-element array in the form [buffer_km_x buffer_km_y].
Z = itslive_data(..., year=years) specifies desired years for annual mosaics. If years are not specified, only the climatology mosaic is loaded. If multiple years are specified, the output Z is a data cube whose third dimension corresponds to each specified year.
Z = itslive_data(..., filepath=path) specifies a directory where the velocity mosaic data reside.
[Z,x,y] = itslive_data(...) also returns map coordinates x,y when three outputs are requested.
[Z,Lat,Lon] = itslive_data(...,geoout=true) returns 2D grids Lat,Lon of geographic coordinates corresponding to each pixel in Z 1. Note that for large grids such as all of Antarctica at full resolution, the coordinate transformation might take several seconds to compute.
Plot a summary mosaic of Iceland:
[v,x,y] = itslive_data(6, 'v');
figure
h = imagesc(x,y,v);
h.AlphaData = isfinite(v); % Makes missing data transparent.
axis xy image % orients and scales properly
set(gca,'colorscale','log')
clim([1 1e3]) % sets color axis limits
exportgraphics(gcf,'itslive_data_documentation_iceland.jpg')
Load all the data in the Pine Island Glacier basin. PIG is in Antarctica,
so we specify region 19. (This example uses plotps from Antarctic Mapping Tools and basin_data from Antarctic boundaries.)
[lat,lon] = basin_data('imbie refined','pine island');
[v,x,y] = itslive_data(19, 'v', latlim=lat, lonlim=lon);
figure
h = imagesc(x,y,v);
h.AlphaData = isfinite(v);
axis xy image
hold on
plotps(lat,lon,'k') % AMT function
set(gca,'colorscale','log')
clim([1 2e3])
cb = colorbar;
ylabel(cb,'Ice speed m yr^{-1})')
exportgraphics(gcf,'itslive_data_documentation_pig.jpg')
Same as above, but this time add a 25 km buffer on all sides and only load data for the year 2019:
[lat,lon] = basin_data('imbie refined','pine island');
[v,x,y] = itslive_data(19, 'v', latlim=lat, lonlim=lon, buffer=25, year=2019);
figure
h = imagesc(x,y,v);
h.AlphaData = isfinite(v);
axis xy image
hold on
plotps(lat,lon,'k')
clim([1 2e3])
cb = colorbar;
ylabel(cb,'Ice speed m yr^{-1})')
exportgraphics(gcf,'itslive_data_documentation_big_pig.jpg')
Consider four points along Malaspina Glacier, Alaska, which are used as an example in the ITS_LIVE widget.
Use the itslive_data function to load data for Region 1 (Alaska) surrounding the four points of interest. Add a 35 km buffer around the four points to provide a little extra context. And load the data for all the years from 2014 through 2022.
Below I'm using the geo2itslive function to transform geo coordinates to projected meters for Region 1 1. The geo2itslive requires MATLAB's Mapping Toolbox. If you don't have that, you can transform the coordinates for Region 1 into EPSG 3413 using the ll2psn function in Arctic Mapping Tools.
% Define locations and years of interest:
lati = [60.08343 60.02582 59.92546 59.83722];
loni = [-140.46707 -140.57831 -140.72388 -140.80765];
years = 2014:2022;
% Transform from geo coordinates to Region 1 projected map coordinates:
[xi, yi] = geo2itslive(1, lati, loni);
% Load velocity data:
[v, x, y] = itslive_data(1,'v',...
latlim=lati,...
lonlim=loni,...
buffer=35, ...
year=years); Now plot the first time slice of the velocity data cube, which corresponds to the first year in our array, 2014. Below, I'm plotting an optional basemap underneath everything, and you can get that function from my plot_basemap repository.
figure
h = imagesc(x,y,v(:,:,1));
h.AlphaData = isfinite(v(:,:,1)); % makes NaNs transparent
axis xy image % orients and scales the axes properly
axis off % removes labels
hold on
plot(xi,yi,'wp','markersize',12) % plots four points as white pentagrams
set(gca,'colorscale','log')
cb = colorbar;
ylabel(cb,'Ice speed (m yr^{-1})')
clim([5 5e3]) % sets color axis limits
title(num2str(years(1)),'fontweight','bold')
bm = plot_basemap('epsg',3413); % optional basemap
exportgraphics(gcf,'itslive_data_documentation_malaspina.jpg')
Creating the animation below requires my gif function. The first call to gif initializes the file and the subsequent calls each add a frame.
gif('itslive_data_demo.gif','DelayTime',1/4)
% Update the plot for the remaining years:
for k = 2:length(years)
h.CData = v(:,:,k);
h.AlphaData = isfinite(v(:,:,k));
title(num2str(years(k)),'fontweight','bold')
gif % adds a gif frame
end
The MATLAB functions in this repo and this documentation were written by Chad A. Greene of NASA/JPL. The NASA MEaSUREs ITS_LIVE project is by Alex S. Gardner and the ITS_LIVE team.