Cloud mask
Dataset description
The cloud mask was derived from radiance measurements of the SWIR camera of the specMACS instrument. To overcome the effects of the sunglint, spectral water vapor absorption was used to identify clouds in front of a bright background. The cloud mask for each research flight is stored in a seperate NETCDF4 file. Each file contains the following variables:
- ”cloud_mask”: binary cloud mask where 0 indicates clear and 1 cloudy pixels.
- ”swir_1600nm_radiance”: radiance measured by the SWIR camera at a wavelength of 1600 nm in units of [mW m-2 nm-1 sr-1] (data were smoothed by a gaussian 3x3 kernel to minimize inconsitencies in the measurements and obtain a decent result for the cloud mask)
- ”viewing_zenith_angle”: angle between the the local vertical axis with respect to the WGS 84 ellipsoid and each camera pixel. The angle is given in [degree]
- ”ice_mask”: binary mask where 0 means that the window of the instrument housing was not iced and 1 means that the window was iced when the measurement took place.
Important note: the icing of the window can introduce a bias in the cloud mask in the iced section (more/less clouds are detected). Ice affected parts should therefore be handeled carefully.
Download
If you want to access the data of all research flights at once via OPeNDAP, you can use this xarray command:
import xarray as xr
ds = xr.open_mfdataset(["https://macsserver.physik.uni-muenchen.de/products/dap/narval-ii/cloudmask/specMACS_cloudmask_narval2_201608{:02d}.nc".format(i) for i in [10,12,15,17,19,22,24,26]])
Literature
- The algorithm developed to extract the cloud mask from the specMACS data in the presence of sunglint is described in the Master's Thesis of Felix Gödde.
The Pdf document of the thesis can be downloaded here.
- A comparison of cloud masks derived from different instruments during NARVAL-II is shown in the Bachelor Thesis of Sabrina Pavicic.
The Pdf document of the thesis can be downloaded here.