According to the linked article (article is in English; only the video is in Japanese):
If the time difference caused by slightly differing gravity levels at different altitudes can be measured precisely, that could lead to the development of technology to accurately estimate the difference in height based on the time lag.
“I want to take the first step toward a paradigm change to measure the height based on the theory of relativity,” said Hidetoshi Katori, 54, an engineering professor at the university.
