Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies
Spaceborne LiDAR altimetry has been demonstrated to be an essential source of data for the estimation and monitoring of inland water level variations. In this study, water level estimates from the Global Ecosystem Dynamics Investigation (GEDI) were validated against in situ gauge station records ove...
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| Format: | Article |
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MDPI AG
2022-01-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/14/2/340 |
| _version_ | 1797490654500093952 |
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| author | Ibrahim Fayad Nicolas Baghdadi Frédéric Frappart |
| author_facet | Ibrahim Fayad Nicolas Baghdadi Frédéric Frappart |
| author_sort | Ibrahim Fayad |
| collection | DOAJ |
| description | Spaceborne LiDAR altimetry has been demonstrated to be an essential source of data for the estimation and monitoring of inland water level variations. In this study, water level estimates from the Global Ecosystem Dynamics Investigation (GEDI) were validated against in situ gauge station records over Lake Geneva for the period between April 2019 and September 2020. The performances of the first and second releases (V1 and V2, respectively) of the GEDI data products were compared, and the effects on the accuracy of the instrumental and environmental factors were analyzed in order to discern the most accurate GEDI acquisitions. The respective influences of five parameters were analyzed in this study: (1) the signal-over-noise ratio (<i>SNR</i>); (2) the width of the water surface peak within the waveform (<i>gwidth</i>); (3) the amplitude of the water surface peak within the waveform (A); (4) the viewing angle of GEDI (<i>VA</i>); and (5) the acquiring beam. Results indicated that all these factors, except the acquiring beam, had an effect on the accuracy of GEDI elevations. Nonetheless, using <i>VA</i> as a filtering criterion was demonstrated to be the best compromise between retained shot count and water level estimation accuracy. Indeed, by choosing the shots with a <i>VA</i> ≤ 3.5°, 74.6% of the shots (after an initial filter) were retained with accuracies similar to choosing A > 400 (46.2% retained shots), <i>SNR</i> > 15 dB (63.3% retained shots), or <i>gwidth</i> < 10 bins (46.5% of retained shots). Finally, the comparison between V1 and V2 elevations showed that V2, overall, provided elevations with a more constant, but higher, bias and fewer deviations to the in situ data than V1. Indeed, by choosing GEDI shots with <i>VA</i> ≤ 3.5°, the unbiased RMSE (ubRMSE) of GEDI elevations was 27.1 cm with V2 (r = 0.66) and 42.8 cm with V1 (r = 0.34). Results also show that the accuracy of GEDI (ubRMSE) does not seem to depend on the beam number and GEDI acquisition dates for the most accurate GEDI acquisitions (<i>VA</i> ≤ 3.5°). Regarding the bias, a higher value was observed with V2, but with lower variability (54 cm) in comparison to V1 (35 cm). Finally, the bias showed a slight dependence on beam GEDI number and strong dependence on GEDI dates. |
| first_indexed | 2024-03-10T00:36:06Z |
| format | Article |
| id | doaj.art-1fd1a53a7938474bbda38e3af185a65f |
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| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T00:36:06Z |
| publishDate | 2022-01-01 |
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| spelling | doaj.art-1fd1a53a7938474bbda38e3af185a65f2023-11-23T15:16:07ZengMDPI AGRemote Sensing2072-42922022-01-0114234010.3390/rs14020340Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland WaterbodiesIbrahim Fayad0Nicolas Baghdadi1Frédéric Frappart2TETIS, University of Montpellier, AgroParisTech, CIRAD, CNRS, INRAE, 34090 Montpellier, FranceTETIS, University of Montpellier, AgroParisTech, CIRAD, CNRS, INRAE, 34090 Montpellier, FranceLEGOS, University of Toulouse, CNES, CNRS, IRD, UPS, 14 avenue Edouard Belin, 31400 Toulouse, FranceSpaceborne LiDAR altimetry has been demonstrated to be an essential source of data for the estimation and monitoring of inland water level variations. In this study, water level estimates from the Global Ecosystem Dynamics Investigation (GEDI) were validated against in situ gauge station records over Lake Geneva for the period between April 2019 and September 2020. The performances of the first and second releases (V1 and V2, respectively) of the GEDI data products were compared, and the effects on the accuracy of the instrumental and environmental factors were analyzed in order to discern the most accurate GEDI acquisitions. The respective influences of five parameters were analyzed in this study: (1) the signal-over-noise ratio (<i>SNR</i>); (2) the width of the water surface peak within the waveform (<i>gwidth</i>); (3) the amplitude of the water surface peak within the waveform (A); (4) the viewing angle of GEDI (<i>VA</i>); and (5) the acquiring beam. Results indicated that all these factors, except the acquiring beam, had an effect on the accuracy of GEDI elevations. Nonetheless, using <i>VA</i> as a filtering criterion was demonstrated to be the best compromise between retained shot count and water level estimation accuracy. Indeed, by choosing the shots with a <i>VA</i> ≤ 3.5°, 74.6% of the shots (after an initial filter) were retained with accuracies similar to choosing A > 400 (46.2% retained shots), <i>SNR</i> > 15 dB (63.3% retained shots), or <i>gwidth</i> < 10 bins (46.5% of retained shots). Finally, the comparison between V1 and V2 elevations showed that V2, overall, provided elevations with a more constant, but higher, bias and fewer deviations to the in situ data than V1. Indeed, by choosing GEDI shots with <i>VA</i> ≤ 3.5°, the unbiased RMSE (ubRMSE) of GEDI elevations was 27.1 cm with V2 (r = 0.66) and 42.8 cm with V1 (r = 0.34). Results also show that the accuracy of GEDI (ubRMSE) does not seem to depend on the beam number and GEDI acquisition dates for the most accurate GEDI acquisitions (<i>VA</i> ≤ 3.5°). Regarding the bias, a higher value was observed with V2, but with lower variability (54 cm) in comparison to V1 (35 cm). Finally, the bias showed a slight dependence on beam GEDI number and strong dependence on GEDI dates.https://www.mdpi.com/2072-4292/14/2/340LiDARGEDIaltimetrylakesProduct V001Product V002 |
| spellingShingle | Ibrahim Fayad Nicolas Baghdadi Frédéric Frappart Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies Remote Sensing LiDAR GEDI altimetry lakes Product V001 Product V002 |
| title | Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies |
| title_full | Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies |
| title_fullStr | Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies |
| title_full_unstemmed | Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies |
| title_short | Comparative Analysis of GEDI’s Elevation Accuracy from the First and Second Data Product Releases over Inland Waterbodies |
| title_sort | comparative analysis of gedi s elevation accuracy from the first and second data product releases over inland waterbodies |
| topic | LiDAR GEDI altimetry lakes Product V001 Product V002 |
| url | https://www.mdpi.com/2072-4292/14/2/340 |
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