Quantification of uncertainty caused by geometric location mismatch in the validation of TROPOMI solar-induced chlorophyll fluorescence product

ABSTRACT

Validation of the TROPOspheric Monitoring Instrument (TROPOMI) SIF product is a necessity to evaluate its feasibility in various applications. A few validation works have been conducted through direct comparison with in-situ SIF retrievals or cross-comparison with similar satellite-based SIF or vegetation index (VI) products. Nevertheless, the influence of the geolocation mismatch between the validation pixel and reference data on validation results was never considered. This study, for the first time, quantifies the geolocation shift of the TROPOMI validation pixel based on a geometric location matching method and then the uncertainty caused by the geolocation mismatch. The results indicate that the geolocation shift of the TROPOMI pixel shows large temporal variations, with a standard deviation of 2.30 km and 1.91 km in the across- and along-track directions. The mean shifts are 0.17 km and 0.28 km in the across- and along-track directions respectively, indicating eastward shifts in the across-track direction and northward shifts in the along-track direction in general. More than half (42/54) of the time periods showed relative uncertainty larger than 5%, with the maximum even reaching 55.7%. Hence, the uncertainty caused by geolocation mismatch should be fully considered in the validation of satellite SIF products, especially over heterogeneous surfaces.

KEYWORDS:

• TROPOMI SIF
• geometric error
• uncertainty
• heterogeneous surface
• validation

Acknowledgments

We gratefully acknowledge the anonymous reviewers and editor of the paper for providing critical and constructive comments, which have helped us to significantly improve the manuscript. We also appreciate the assistance of the all authors of this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the website given in the manuscript.

Additional information

Funding

This research was jointly supported by the National Natural Science Foundation of China (Grant No. 42071296), and the Fundamental Research Funds for the Central Universities (lzujbky-2022-09).