L3

4.7. L3#

The Level 3 altimeter dataset represents a simplified version of the L2P. Along-track measurements from different missions are merged together into single daily multi-mission files and only key variables are kept. The L2P measurements lower than 3 (good quality) are discarded in the L3 which only contains the best quality measurements. This dataset is intended for users who only care about SWH values.

For altimeters, only the Ku band measurements are considered, when available (the only current exception being SARAL for which only Ka band is provided).

This section describes in detail the specific content of the version 4 L3 dataset, configured as shown in the table Table 4.60, which can be used to locate the appropriate detailed information in this document.

Table 4.60 Summary description of the contents of a CCI Sea State L3 data product#
netCDF File Contents	Description
Coordinate variables	Information to permit locating data on non-orthogonal grids, as defined in Section 3.2
Geophysical data record variables	environmental variables for 1st band altimeter (usually Ku) as defined in Section 4.7.1
Traceability data record variables	traceability variables to source measurements as defined in Section 4.7.2
Global Attributes	A collection of required global attributes describing general characteristics of the file, as defined in section Section 3.3

4.7.1. L3 geophysical data record format specification#

The Table 4.61 provides an overview of the CCI Sea State L3 environmental data records together with a link to their detailed description.

Table 4.61 Summary description of CCI Sea State L3 SWH environmental records#
Variable Name	Description	Units
swh	Significant wave height, as retrieved from the altimeter retracker, averaged over 1 Hz cells, without bias correction.	m
swh_adjusted	Significant wave height, averaged over 1 Hz cells, with cross-mission bias correction.	m
swh_denoised	Significant wave height, averaged over 1 Hz cells, with cross-mission bias correction and denoising.	m
swh_uncertainty	Uncertainty of the significant wave height averaged over 1 Hz cells.	1

4.7.2. L3 traceability data record format specification#

The Table 4.62 provides an overview of the variables that detail the source and context of each SWH measurement.

Table 4.62 Summary description of CCI Sea State L4 traceability records#
Variable Name	Description	Units
satellite	Mean of median significant wave height values	code
cycle	Maximum median significant wave height value	int
relative_pass	RMS of median significant wave height values	int

4.7.2.1. `satellite`#

This variable provides the identifier of the satellite from which a SWH measurement originates. The identifier is one of the following enumerate code:

value	satellite mission
0	Cryosat-2
1	Jason-1
2	Jason-2
3	Jason-3
4	Saral
5	Sentinel-3 A
6	ENVISAT
7	Topex-Poseidon
8	ERS-1
9	ERS-2
10	Ssentinel-3 B
11	Sentinel-6 A

Table 4.63 CDL example description of **satellite** variable#
Storage type	Name	Unit
float	`satellite`	code

ubyte satellite(time) ;
	satellite:long_name = "satellite associated with measurement" ;
	satellite:flag_values = 0UB, 1UB, 2UB, 3UB, 4UB, 5UB, 6UB, 7UB, 8UB, 9UB, 10UB, 11UB ;
	satellite:flag_meanings = "cryosat-2 jason-1 jason-2 jason-3 saral sentinel-3_a envisat topex-poseidon ers-1 ers-2 sentinel-3_b sentinel-6_a" ;
	satellite:coverage_content_type = "auxiliaryInformation" ;
	satellite:coordinates = "lat lon" ;

4.7.2.2. `cycle`#

The number of the satellite cycle a given SWH measurement originates from. Note that this information may not be available for all satellite missions.

Table 4.64 CDL example description of **cycle** variable#
Storage type	Name	Unit
float	`cycle`	int

ushort cycle(time) ;
	cycle:coverage_content_type = "auxiliaryInformation" ;
	cycle:long_name = "cycle number of satellite associated with measurement" ;
	cycle:coordinates = "lat lon" ;

4.7.2.3. `relative_pass`#

The number of the satellite relative pass with a cycle a given SWH measurement originates from. Note that this information may not be available for all satellite missions.

Table 4.65 CDL example description of **relative_pass** variable#
Storage type	Name	Unit
float	`relative_pass`	int

ushort relative_pass(time) ;
	relative_pass:_FillValue = 0US ;
	relative_pass:coverage_content_type = "auxiliaryInformation" ;
	relative_pass:long_name = "relative pass number of satellite associated with measurement" ;
	relative_pass:coordinates = "lat lon" ;

4.7.3. L3 auxiliary data record format specification#

The Table 4.66 provides an overview of the auxiliary data record within a L3 file together with a link to their detailed description.

Table 4.66 Summary description of CCI Sea State L3 ancillary data records#
Variable Name	Description	Units
distance_to_coast	Distance to the nearest shoreline	m
bathymetry	Water depth to sea floor	m

L3

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