Geodetic Data Collection Techniques - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 64

surface, and A e denotes horizontal acceleration, the inclination correction to the
horizontal acceleration (A h ) can be expressed as:

A h ¼ g cos ð ʸ 1 Þ þ A e sin ʸ: ð 2 : 31 Þ

3. 4 0 , A b is less than 1 mGal.
Since the horizontal precision of the gyro platform is better than 0. 2 0 , this correc-
tion is generally neglected and the corresponding error is less than 0.05 mGal.

In the above equation, when A e ¼ 500 mGal, ʸ

System of Airborne Gravimetry

The airborne gravimetry system is the product of a combination of modern tech-
nologies like gravity sensing, satellite positioning, inertia and precision altimetry,
etc. It mainly consists of five systems:

1. Gravity Sensor System. This mainly comprises the airborne gravimeter and the
platform. The airborne gravimeter should have enough dynamic range and be
able to provide information, like the large, short-time accelerations while the
aircraft is taking off and landing, so as to facilitate the computation of correc-
tions to the gravity disturbance.
2. Dynamic Positioning System. The major role of this system is to guarantee the
optimal real-time navigation by using GPS, to provide data of initial orbit and
precise location, and to compute accelerations in relation to the motion of the
carriers. It is feasible to use merely pseudo-range measurement in real-time
navigation. However, in order to obtain the precise flight path, it is necessary to
integrate the utilization of pseudo-range measurement, phase measurement, and
Doppler measurement to observe data.
3. Attitude Sensor System. The flight attitude of the aircraft is usually referred to as
“pitch, roll, and yaw” and is determined by inertia measuring instruments.
Because of the disadvantages that inertia measuring instruments are highly
expensive, suffer from high drift, and are hard to maintain, in recent years
GPS attitude measuring instruments with high precision, zero drift, and low
price have come into use.
4. Altitude Sensor System. The major function of this system is to provide data on
height for computing the E¨ tv¨s correction. The correction is applied to reduce
the airborne gravity anomaly to the Earth's surface using microwave altimeter,
radar altimeter, pressure altimeter, or GPS survey.
5. Data Collection and Processing System. This includes airborne data collection
devices and ground data processing devices. The airborne devices are used to
record the input data from the subsystems of the gravity sensor, navigation
positioning, attitude sensor, and altitude sensor in synchronization. Each set of
recorded data should have a unified accurate time scale to facilitate computation
and processing for the ground devices.