Hi Helle,

The problem with HYCOM is that the bottom layer of their 4D array does not correspond to the seafloor—it corresponds to a depth of 5500m. Each vertical layer of HYCOM corresponds to a fixed depth: 0, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1750, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500. Where the seafloor is shallower than a layer’s depth, the layer does not have any data there. So, to assemble a raster layer that represents the temperature at the seafloor, one must overlay multiple layers and, for each 2D cell, select the value from the deepest layer with data.

MGET performs this job automatically if you put in 20000 for the Minimum Depth and Maximum Depth parameters, under the Spatiotemporal Extent options of the tool. Are you doing that? If not—if you leave those parameters empty—the tool will create rasters for all depth layers. This will go quite slow. If you put in the 20000, it will only create rasters for that “seafloor” layer and will go somewhat faster, but it might not be dramatically faster because it still has to download many of the layers to obtain values for all cells in your spatial extent of interest. If the spatial extent includes land or shallow areas, it may have to download all the layers.

Also, if you have not specified a Spatial Extent, you should definitely do that; otherwise it will download a global image, which may not be necessary.

I hope that helps!

Jason

Hi

I am trying to download some ocean data from Hycom. The dataset do not cover a very large area but the forecast is that it will be downloaded some time in Deceber. It is a bit long to wait J

I only need the data-layer nearest the bottom – the bottom layer. It is not possible just to take one “slice” of the data as I work with bottom invertebrates and the layer nearest the bottom will vary with the topography.

Is there any way to subset the data from e.g. Hycom so that I only get the layer nearest the bottom?

This seems to be a recurring problem for biologists who are not R-wizards (judged from the number of questions popping up on the internet).

Best,

Helle