How can I make geotiffs of individual depth layers in the Hycom ocean circulation models?

Question

I am trying to pull layers from the glocal ocean circulation model Hycom. Before I go writing code to try to do this, is there a way to pull a single z depth as a geotiff?

e.g. I have hycom_glb_911_2015093000_t000_uv3z.nc. gdalinfo (gdal pre 2.1.0) reports:

gdalinfo hycom_glb_911_2015093000_t000_uv3z.nc

Driver: netCDF/Network Common Data Format
Files: hycom_glb_911_2015093000_t000_uv3z.nc
Size is 512, 512
Coordinate System is `'
Metadata:
  NC_GLOBAL#classification_authority=not applicable
  NC_GLOBAL#classification_level=UNCLASSIFIED
  NC_GLOBAL#Conventions=CF-1.0 NAVO_netcdf_v1.0
  NC_GLOBAL#distribution_statement=Approved for public release. Distribution unlimited.
  NC_GLOBAL#downgrade_date=not applicable
  NC_GLOBAL#field_type=instantaneous
  NC_GLOBAL#history=archv2ncdf3z
  NC_GLOBAL#institution=Naval Oceanographic Office
  NC_GLOBAL#source=HYCOM archive file
Subdatasets:
  SUBDATASET_1_NAME=NETCDF:"hycom_glb_911_2015093000_t000_uv3z.nc":water_u
  SUBDATASET_1_DESC=[1x40x2001x4500] eastward_sea_water_velocity (16-bit integer)
  SUBDATASET_2_NAME=NETCDF:"hycom_glb_911_2015093000_t000_uv3z.nc":water_v
  SUBDATASET_2_DESC=[1x40x2001x4500] northward_sea_water_velocity (16-bit integer)
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,  512.0)
Upper Right (  512.0,    0.0)
Lower Right (  512.0,  512.0)

ncdump:

ncdump -h hycom_glb_911_2015093000_t000_uv3z.nc 
netcdf hycom_glb_911_2015093000_t000_uv3z {
dimensions:
    lat = 2001 ;
    lon = 4500 ;
    depth = 40 ;
    time = UNLIMITED ; // (1 currently)
variables:
    double time(time) ;
        time:long_name = "Valid Time" ;
        time:units = "hours since 2000-01-01 00:00:00" ;
        time:time_origin = "2000-01-01 00:00:00" ;
        time:calendar = "gregorian" ;
        time:axis = "T" ;
        time:NAVO_code = 13 ;
    double tau(time) ;
        tau:long_name = "Tau" ;
        tau:units = "hours since analysis" ;
        tau:time_origin = "2015-09-30 00:00:00" ;
        tau:NAVO_code = 56 ;
    double depth(depth) ;
        depth:long_name = "Depth" ;
        depth:standard_name = "depth" ;
        depth:units = "m" ;
        depth:positive = "down" ;
        depth:axis = "Z" ;
        depth:NAVO_code = 5 ;
    double lat(lat) ;
        lat:long_name = "Latitude" ;
        lat:standard_name = "latitude" ;
        lat:units = "degrees_north" ;
        lat:point_spacing = "even" ;
        lat:axis = "Y" ;
        lat:NAVO_code = 1 ;
    double lon(lon) ;
        lon:long_name = "Longitude" ;
        lon:standard_name = "longitude" ;
        lon:units = "degrees_east" ;
        lon:modulo = "360 degrees" ;
        lon:axis = "X" ;
        lon:NAVO_code = 2 ;
    short water_u(time, depth, lat, lon) ;
        water_u:long_name = "Eastward Water Velocity" ;
        water_u:standard_name = "eastward_sea_water_velocity" ;
        water_u:units = "m/s" ;
        water_u:_FillValue = -30000s ;
        water_u:missing_value = -30000s ;
        water_u:scale_factor = 0.001f ;
        water_u:add_offset = 0.f ;
        water_u:NAVO_code = 17 ;
    short water_v(time, depth, lat, lon) ;
        water_v:long_name = "Northward Water Velocity" ;
        water_v:standard_name = "northward_sea_water_velocity" ;
        water_v:units = "m/s" ;
        water_v:_FillValue = -30000s ;
        water_v:missing_value = -30000s ;
        water_v:scale_factor = 0.001f ;
        water_v:add_offset = 0.f ;
        water_v:NAVO_code = 18 ;

// global attributes:
        :classification_level = "UNCLASSIFIED" ;
        :distribution_statement = "Approved for public release. Distribution unlimited." ;
        :downgrade_date = "not applicable" ;
        :classification_authority = "not applicable" ;
        :institution = "Naval Oceanographic Office" ;
        :source = "HYCOM archive file" ;
        :history = "archv2ncdf3z" ;
        :field_type = "instantaneous" ;
        :Conventions = "CF-1.0 NAVO_netcdf_v1.0" ;

Answer 1

You can use gdal_translate (NetCDF documentation) for this. I didn't download your dataset but I tested on a sample. The trick is to type in the name f the resource exactly as it's listed in gdalinfo. For example:

gdal_translate NETCDF:"hycom_glb_911_2015093000_t000_uv3z.nc":water_v water_v.tif

This gives you a GeoTiff with the water_v subdataset.