import xarray as xr
url = 'http://gamone.whoi.edu/thredds/dodsC/coawst_4/use/fmrc/coawst_4_use_best.ncd'
ds = xr.open_dataset(url)
ds['h']
<xarray.DataArray 'h' (eta_rho: 336, xi_rho: 896)> [301056 values with dtype=float64] Coordinates: lon_rho (eta_rho, xi_rho) float64 ... lat_rho (eta_rho, xi_rho) float64 ... Dimensions without coordinates: eta_rho, xi_rho Attributes: units: meter long_name: bathymetry at RHO-points field: bath, scalar _ChunkSizes: [336 896] standard_name: sea_floor_depth
ds['foo'] = ds['h']
ds['foo'].values = ds['h'].values * 2
ds['foo'][10,10].values
array(8048.2596865)
ds['h'][10,10].values
array(4024.12984325)