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摘要
According to the use of different specific force system, airborne gravimetry system can be classified into two-axis platform system, triple-axis platform system and strapdown system. Strapdown airborne gravimetry system has many advantages over platform system, such as small size, light weight and low power dissipation. Lots of progresses in the development of the strapdown airborne scalar gravimeter are achieved over the last decade. Our own first prototype of the strapdown airborne scalar gravimeter (named SGA-WZ01) was developed in 2008 and has been verified by several flight tests. Obviously, it is necessary to design a suitable algorithm model for strapdown airborne gravimetry. Therefore, the algorithm models are compared by using the test data of the SGA-WZ01 in the sea area and their internal accuracy from repeated flight lines for different filter amount was evaluated in this paper.
Two algorithm models for strapdown airborne gravimetry are used in general, namely the models of strapdown inertial scalar gravimetry (SISG) and rotation invariant scalar gravimetry (RISG). The differences of the two models reside in three aspects. The first difference is that the SISG model requires both specific forces and attitude angles as input, while the RISG model requires only specific forces (here both only the inertial units information are considered). The second difference is that the SISG model is a linear form of the specific forces and the RISG model is a square form. The latter form may change the characteristics of the noise signal due to the squaring, e.g. a zero-mean noise will after the squaring have a positive mean value, and hence it may become a potential way to bias the gravity estimates. The third difference is the error models, which are difficult to be quantified and compared directly. Based on two pairs of repeated flights data, the spectral characteristics of gravity disturbances obtained by the two models and the internal accuracy for the two models in different filter amount were compared and analyzed.
The results educed from the real flight data indicated that the power spectral density (PSD) for the gravity disturbances obtained by SISG model and RISG model respectively are almost identical, and there are nearly no gravity signal in the spectral bands above 0.003 Hz. Using cascade Butterworth lowpass filter with cutoff frequency of 100 s, 200 s and 300 s, the mean value and the standard deviation of the gravity disturbance difference between the two models are -0.16 mGal, -0.16 mGal, -0.14 mGal and 0.69 mGal, 0.33 mGal, 0.25 mGal respectively.
With the filter amount of 200 s and 300 s, the standard deviation of the gravity disturbance difference between repeated lines are 1.06 mGal, 0.80 mGal for SISG model and are 1.30 mGal, 1.00 mGal for RISG model respectively. Assuming the observations of the repeated flights are independent, the standard deviations of the gravity disturbance for a single profile are all less than 1.0 mGal with the filter amount of 200 s and 300 s respectively.
1) The results obtained from SISG model and RISG model are similar, but the internal accuracy estimated from repeated lines data indicates that the SISG method is a little better than the RISG method. The SISG model is suggested. 2) Due to major differences in the error model of the two approaches, the RISG method can be used as an effective reliability check of the SISG method. RISG method has also the advantage that it needs only three mutually perpendicular accelerometers and hence can simplify the system design. 3) The internal accuracy of SISG method based on repeated flights are 1.06 mGal and 0.80 mGal for the filter length of 200 s and 300 s respectively, which implies that the accuracy of the strapdown scalar airborne gravimetry can achieve 1.0 mGal at a resolution of 10 km for the flight velocity of 360 km . h(-1) 4) The causes of the error and the external accuracy for the strapdown scalar airborne gravimetry should be further investigated.
- 出版日期2015-5
- 单位中国人民解放军信息工程大学
