Chapter 19 - Prediction of Earth tide

Abstract

In general, “tide” refers to both the body tide and ocean tide of the Earth. While ocean tide is more widely recognized in public than body tide, Earth tide refers to body tide in solid Earth geosciences. In fact, body tide is the largest periodic perturbation in the solid Earth. A brief sketch of ocean tide is included in this chapter, however, the main concern here is “body tide.” To predict the displacement, gravity, deflection of vertical associated with Earth’s body tide at any specified time epoch at certain place has been an important task in gravity prospecting and gravimetric geodesy. “Love numbers,” which are the three kinds of ratios between the response of real Earth and that of an ideal Earth under tidal force, and are quite conveniently used in body tidal predictions. Accurate Love numbers can only be determined through a numerical computation with the Earth’s physical property model. Another information required for body tide prediction are the positions of the Moon and the Sun. Because tidal force rapidly decreases with distance (1/r3), other planets, even Jupiter, induce negligible amounts of tide (relatively less than 10−5). Therefore it is of utmost importance to have the accurate ephemerides computation algorithm about the two largest tide raising celestial bodies; the Moon and the Sun. In this chapter the method to predict body tide of the Earth is described with emphasis on the two algorithms; (1) to compute Love numbers, and (2) to predict body tidal perturbation using Love numbers and lunar/solar ephemerides. And these are actually the main stems of K2-Tide; an Earth tide prediction computer program. Brief explanations about ocean tide model and load Love number as well as fluid Love number are attached at the end of this chapter.