{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T15:29:17Z","timestamp":1772119757583,"version":"3.50.1"},"reference-count":44,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2024,7,5]],"date-time":"2024-07-05T00:00:00Z","timestamp":1720137600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"The National Natural Science Foundation of China","award":["42174102"],"award-info":[{"award-number":["42174102"]}]},{"name":"The National Natural Science Foundation of China","award":["42192535"],"award-info":[{"award-number":["42192535"]}]},{"name":"The National Natural Science Foundation of China","award":["41931076"],"award-info":[{"award-number":["41931076"]}]},{"name":"The National Natural Science Foundation of China","award":["ZDBS-LY-DQC028"],"award-info":[{"award-number":["ZDBS-LY-DQC028"]}]},{"name":"The National Natural Science Foundation of China","award":["2023AFB366"],"award-info":[{"award-number":["2023AFB366"]}]},{"name":"The Basic Frontier Science Research Program of Chinese Academy of Sciences","award":["42174102"],"award-info":[{"award-number":["42174102"]}]},{"name":"The Basic Frontier Science Research Program of Chinese Academy of Sciences","award":["42192535"],"award-info":[{"award-number":["42192535"]}]},{"name":"The Basic Frontier Science Research Program of Chinese Academy of Sciences","award":["41931076"],"award-info":[{"award-number":["41931076"]}]},{"name":"The Basic Frontier Science Research Program of Chinese Academy of Sciences","award":["ZDBS-LY-DQC028"],"award-info":[{"award-number":["ZDBS-LY-DQC028"]}]},{"name":"The Basic Frontier Science Research Program of Chinese Academy of Sciences","award":["2023AFB366"],"award-info":[{"award-number":["2023AFB366"]}]},{"name":"The Hubei Provincial Science Foundation of China","award":["42174102"],"award-info":[{"award-number":["42174102"]}]},{"name":"The Hubei Provincial Science Foundation of China","award":["42192535"],"award-info":[{"award-number":["42192535"]}]},{"name":"The Hubei Provincial Science Foundation of China","award":["41931076"],"award-info":[{"award-number":["41931076"]}]},{"name":"The Hubei Provincial Science Foundation of China","award":["ZDBS-LY-DQC028"],"award-info":[{"award-number":["ZDBS-LY-DQC028"]}]},{"name":"The Hubei Provincial Science Foundation of China","award":["2023AFB366"],"award-info":[{"award-number":["2023AFB366"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>High-accuracy optical clocks have garnered increasing attention for their potential application in various fields, including geodesy. According to the gravitational red-shift effect, clocks at lower altitudes on the Earth\u2019s surface run slower than those at higher altitudes due to the differential gravitational field. Consequently, the geopotential difference can be determined by simultaneously comparing the frequency of two optical clocks at disparate locations. Here, we report geopotential difference measurements conducted using a pair of transportable 40Ca+ optical clocks with uncertainties at the 10\u221217 level. After calibrating the output frequencies of two optical clocks in the horizontal position, frequency comparison is realized by moving Clock 2 to two different positions using a high-precision optical fiber time\u2013frequency transmission link with Clock 1. The elevation difference of the two different positions, as processed by ensemble empirical mode decomposition (EEMD), is measured as \u221288.4 cm \u00b1 16.7 cm and 104.5 cm \u00b1 20.1 cm, respectively, which is consistent with the geometric measurement results within the error range. This experimental result validates the credibility of the optical clock time\u2013frequency comparison used in determining geopotential differences, thereby providing a novel measurement model for the establishment of a global unified elevation datum.<\/jats:p>","DOI":"10.3390\/rs16132462","type":"journal-article","created":{"date-parts":[[2024,7,5]],"date-time":"2024-07-05T11:46:05Z","timestamp":1720179965000},"page":"2462","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Geopotential Difference Measurement Using Two Transportable Optical Clocks\u2019 Frequency Comparisons"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-1854-7155","authenticated-orcid":false,"given":"Daoxin","family":"Liu","sequence":"first","affiliation":[{"name":"State Key Laboratory of Geodesy and Earth\u2019s Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430077, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6928-6797","authenticated-orcid":false,"given":"Lin","family":"Wu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Geodesy and Earth\u2019s Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430077, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3952-2044","authenticated-orcid":false,"given":"Changliang","family":"Xiong","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Geodesy and Earth\u2019s Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430077, China"},{"name":"University of Chinese Academy of Sciences, Beijing 100049, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7860-888X","authenticated-orcid":false,"given":"Lifeng","family":"Bao","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Geodesy and Earth\u2019s Dynamics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430077, China"},{"name":"University of Chinese Academy of Sciences, Beijing 100049, China"}]}],"member":"1968","published-online":{"date-parts":[[2024,7,5]]},"reference":[{"key":"ref_1","first-page":"570","article-title":"Vertical datum unification for the international height reference system (IHRS)","volume":"209","author":"Sideris","year":"2017","journal-title":"Geophys. 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