Lustrumboek 'The 5th Element" Basically there are two possibilities to counteract the damping effect: first of all, r6onan oli i ^ellite as low as possible. The lowest altitude, however, is limited to ^UU-250 km or technical, financial, and safety reasons, and this is not sufficient to meet the goals given in fiaure 3. The second possibility is indicated in figure 5 I he top panel shows the information content of the second radial derivative of the potential at 250 km altitude. Obviously, this quantity has much more power in the short wavelengths compared to the first derivative (bottom panel of figure 5), which is of course due to the differentiation. Derivatives of the potential are provided by differencing techniques. For instance, second derivatives of the potential can be derived from acceleration differences between two proof masses over very short distances (some decimeters). This is called 'differential accelerometry'. In general, the term 'gravity gradiometry' is used to indicate the measurement of second order potential derivatives. These quantities are much more sensitive to the fine structures of the gravitational field, and this sensitivity increases with decreasing distance between the proof masses. Gravity gradient at 250km altitude SO 120 180 240 Longitude 109 S"2 Gravity anomalies at 250km altitude Figure 5: The attenuation effect counteracted 8

Digitale Tijdschriftenarchief Stichting De Hollandse Cirkel en Geo Informatie Nederland

Lustrumboek Snellius | 2000 | | pagina 21