Evaluation of Sentinel-5P TROPOMI Methane Observations at Northern High Latitudes

• Published in: Remote Sensing
• Main Authors: Hannakaisa Lindqvist, Ella Kivimäki, Tuomas Häkkilä, Aki Tsuruta, Oliver Schneising, Michael Buchwitz, Alba Lorente, Mari Martinez Velarte, Tobias Borsdorff, Carlos Alberti, Leif Backman, Matthias Buschmann, Huilin Chen, Darko Dubravica, Frank Hase, Pauli Heikkinen, Tomi Karppinen, Rigel Kivi, Erin McGee, Justus Notholt, Kimmo Rautiainen, Sébastien Roche, William Simpson, Kimberly Strong, Qiansi Tu, Debra Wunch, Tuula Aalto, Johanna Tamminen
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2024
• Subjects: methane; Arctic; boreal; TROPOMI; permafrost; TCCON; Science; Q
• Online Access: https://doi.org/10.3390/rs16162979; https://doaj.org/article/3f1cdc138c6b42fd8b3a3995c1582c7d

The Arctic and boreal regions are experiencing a rapid increase in temperature, resulting in a changing cryosphere, increasing human activity, and potentially increasing high-latitude methane emissions. Satellite observations from Sentinel-5P TROPOMI provide an unprecedented coverage of a column-averaged dry-air mole fraction of methane (XCH 4 ) in the Arctic, compared to previous missions or in situ measurements. The purpose of this study is to support and enhance the data used for high-latitude research through presenting a systematic evaluation of TROPOMI methane products derived from two different processing algorithms: the operational product (OPER) and the scientific product (WFMD), including the comparison of recent version changes of the products (OPER, OPER rpro, WFMD v1.2, and WFMD v1.8). One finding is that OPER rpro yields lower XCH 4 than WFMD v1.8, the difference increasing towards the highest latitudes. TROPOMI product differences were evaluated with respect to ground-based high-latitude references, including four Fourier Transform Spectrometer in the Total Carbon Column Observing Network (TCCON) and five EM27/SUN instruments in the Collaborative Carbon Column Observing Network (COCCON). The mean TROPOMI–TCCON GGG2020 daily median XCH 4 difference was site-dependent and varied for OPER rpro from −0.47 ppb to 22.4 ppb, and for WFMD v1.8 from 1.2 ppb to 19.4 ppb with standard deviations between 13.0 and 20.4 ppb and 12.5–15.0 ppb, respectively. The TROPOMI–COCCON daily median XCH 4 difference varied from −26.5 ppb to 5.6 ppb for OPER rpro, with a standard deviation of 14.0–28.7 ppb, and from −5.0 ppb to 17.2 ppb for WFMD v1.8, with a standard deviation of 11.5–13.0 ppb. Although the accuracy and precision of both TROPOMI products are, on average, good compared to the TCCON and COCCON, a persistent seasonal bias in TROPOMI XCH 4 (high values in spring; low values in autumn) is found for OPER rpro and is reflected in the higher standard deviation values. A systematic decrease of about 7 ppb was found ...