New L4 production including SWOT-KaRIn swath measurements
A new demonstrative Near-Real-Time (NRT) L4 product has been added to the catalogue. This product merges data from all available nadir altimeters and also integrates SWOT Karin L3 data (AVISO+, 2025; Dibarboure et al., 2025) currently available on the AVISO+ platform. The inclusion of SWOT Karin wide-swath altimetry improves ocean surface topography mapping by reducing mapping errors.
To assess the impact of integrating Karin data into the NRT mapping process, specific experiments were conducted using all available altimeters, except SARAL/Altika that is excluded for validation. The evaluation metrics (mapping error variance at various spatial scales (all scale, < 500km, < 200km) and in different oceanic regimes) are summarized in Table for d0 day, d-3 day, and d-6 day.
The integration of Karin helps to reduce the mapping by 3% to 17% at d0 day. At d-3 day and d-6day, the integration of Karin helps to reduce the mapping error between 10% to 18%.
Table: Mapping errors variances at d0 d-3 and d-6 day in nadirs only L4 product and nadir + Karin L4 product for various oceanic regimes and in considering scale <500km, <200km and all scales
| d0 day nadir only | d0 day nadir + Karin | |||||
| mapping_err_var [cm²] | mapping_err_filtered_65-500km_var [cm²] | mapping_err_filtered_65-200km_var [cm²] | mapping_err_var [cm²] | mapping_err_filtered_65-500km_var [cm²] | mapping_err_filtered_65-200km_var [cm²] | |
| coastal | 35.2 | 7.4
|
2.6 | 34.2 (-3%) | 7.4 (+0%) | 2.6 (0%) |
| offshore_highvar | 67.3
|
23.0 | 8.0
|
57.7 (-14%) | 19.2 (-17%) | 6.9 (-14%) |
| offshore_lowvar | 17.0 | 3.4 | 1.4 | 15.7 (-8%) | 3.0 (-12%) | 1.2 (-14%) |
| equatorial_band | 20.5 | 3.5 | 1.4 | 19.4 (-5%) | 3.5 (-1%) | 1.4
(0%) |
| d-3 day nadir only | d-3 day nadir + Karin | |||||
| coastal | 26.6 | 5.6 | 2.1 | 26.6 (0%) | 5.6(0%) | 2.1(0%) |
| offshore_highvar | 31.0 | 8.4 | 3.7 | 27.6(-11%) | 6.9(-18%) | 3.2(-14%) |
| offshore_lowvar | 13.1 | 2.3 | 1.0 | 12.5(-5%) | 2.1(-9%) | 0.9 (-10%) |
| equatorial_band | 16.0 | 3.1 | 1.3 | 16.0(0%) | 3.1(0%) | 1.3(0%) |
| d-6 day nadir only | d-6 day nadir + Karin | |||||
| coastal | 25.9 | 5.3 | 2.1 | 26.0 (0%) | 5.3(0%) | 2.0 (-5%) |
| offshore_highvar | 27.4 | 7.2 | 3.5 | 25.4(-7%) | 6.2(-14%) | 3.1(-11%) |
| offshore_lowvar | 12.5 | 2.1 | 1.0 | 12.2(-2%) | 2.0(-4%) | 0.9(-10%) |
| equatorial_band | 15.6 | 3.1 | 1.3 | 15.7 (+1%) | 3.1(0%) | 1.3(0%) |