Algorithm Input and Output Data Definition

The Algorithm Input and Output Data Definition (IODD) is described hereafter. Except for the input L1b TB data, all auxiliary and output data follow the EASE-Grid 2.0 polar projection of the Northern Hemisphere with a preliminary target spatial resolution of 3.125km.

Input Data

Daily brightness temperature data are the main input, namely Ku-band data of horizontal polarisation and Ka-band data of both polarisations.

Input L1 Data

Field	Description	Shape/Amount
L1b TB Ku-band	L1B Brightness Temperatures at 18.7 GHZ (H polarisation)	Full swath or swath section (Nscans,Npos)
L1b TB Ka-band	L1B Brightness Temperatures at 36.5 GHZ (H and V polarisation)	Full swath or swath section (Nscans,Npos)

Important

If available, night or morning acquisition times are preferred over afternoon or evening brightness temperature data, in order to minimise effects of liquid water within the snowpack due to melt.

Auxiliary data

Although the application of auxiliary data is not required to run the TSA algorithm per se, it is highly recommended to mask out known large water bodies to ensure satisfactory product quality. The use of an internal mask is recommended for consistency among all L2 products. Further internal or external auxiliary data files (ADF) are to be determined.

Field	Description	Shape/Amount
Water Mask	Binary mask of large water bodies, incl. oceans and lakes	EASE-Grid 2.0 NH (nx,ny)

Input L2 Data

The TSA algorithm does not require fields from other L2 processors as input.

Output Data

Output variables generated by the L2 TSA processor encompass the TSA map, corresponding uncertainty estimates and complementary status information.

Field	Description	Shape/Amount
TSA	Terrestrial Snow Area (TSA)	EASE-Grid 2.0 NH (nx,ny)
TSA Uncertainty	Qualitative uncertainty of TSA variable: ‘0: very likely snow-free (FWD & BCK); 1: likely snow (FWD	BCK); 2: very likely snow (FWD & BCK)’
Status Flag	Status flag for TSA	EASE-Grid 2.0 NH (nx,ny)

The main TSA variable (tsa) is a binary mask indicating snow-free pixels as 0, and snow-covered pixels as 1. The TSA uncertainty (tsa_uncertainty) in turn is described through an 8-bit mask with the following allocated values:

Bit	Description
0	Very likely snow free
1	Likely snow covered
2	Very likely snow covered

The status flag (status_flag) similarly is an 8-bit mask with the following allocated values:

Bit	Description
0	Water
1	Land
2	Dry snow (valid)
3-7	Placeholders
8	No data, out of grid

Note

Empty placeholders within the status flag may be used for future research activities, such as the development of a wet snow flag.