Strapdown Airborne Gravimeter Research Articles

A New Method for Determining the Gravity Disturbance Vector in Strapdown Airborne Gravimetry

A two-step method for determining the gravity disturbance vector based on strapdown airborne gravimeter (SAG) and Global navigation satellite system (GNSS) is proposed. First, a strapdown navigation algorithm and a Kalman filter are used to estimate and compensate for the biases of the accelerometers by the maneuvering flight of SAG. Second, the gravity disturbance vector equations of SAG are established, and the forward and smoothing Kalman filter tuned by the formula of the gravity parameter in the Markov stochastic process are used to estimate the gravity disturbance vector, the model of which is described by the second-order Markov stochastic process to separated it from the biases of the accelerometers. The validity of the above method is verified by processing the data of the repeated line flight test of SAG in the South China Sea, and the results reveal that the internal coincidence accuracy of gravity anomaly is better than 0.4 mGal, and that of the horizontal gravity disturbance is better than 2 mGal.

Optimized Design of the SGA-WZ Strapdown Airborne Gravimeter Temperature Control System.

The temperature control system is one of the most important subsystems of the strapdown airborne gravimeter. Because the quartz flexible accelerometer based on springy support technology is the core sensor in the strapdown airborne gravimeter and the magnet steel in the electromagnetic force equilibrium circuits of the quartz flexible accelerometer is greatly affected by temperature, in order to guarantee the temperature control precision and minimize the effect of temperature on the gravimeter, the SGA-WZ temperature control system adopts a three-level control method. Based on the design experience of the SGA-WZ-01, the SGA-WZ-02 temperature control system came out with a further optimized design. In 1st level temperature control, thermoelectric cooler is used to conquer temperature change caused by hot weather. The experiments show that the optimized stability of 1st level temperature control is about 0.1 °C and the max cool down capability is about 10 °C. The temperature field is analyzed in the 2nd and 3rd level temperature control using the finite element analysis software ANSYS. The 2nd and 3rd level temperature control optimization scheme is based on the foundation of heat analysis. The experimental results show that static accuracy of SGA-WZ-02 reaches 0.21 mGal/24 h, with internal accuracy being 0.743 mGal/4.8 km and external accuracy being 0.37 mGal/4.8 km compared with the result of the GT-2A, whose internal precision is superior to 1 mGal/4.8 km and all of them are better than those in SGA-WZ-01.

Progress in the development of Laser Strapdown Airborne Gravimeter in China

Based on laser gyros and quartz flexure accelerometers, Beijing Institute of Aerospace Control Devices has developed the prototype of Laser Strapdown Airborne Gravimeter (LSAG). The hardware improvements and the design of post-processing software are presented, and field test results of the system on the aircraft and oceanic vessel during 2013 and 2014 are given. Field test results showed that the internal accord accuracy after level adjustment was about 1mGal, demonstrating that LSAG has the abilities to implement airborne gravity surveys, and has the potential for marine gravity surveys.

A Flight Test of the Strapdown Airborne Gravimeter SGA-WZ in Greenland

An airborne gravimeter is one of the most important tools for gravity data collection over large areas with mGal accuracy and a spatial resolution of several kilometers. In August 2012, a flight test was carried out to determine the feasibility and to assess the accuracy of the new Chinese SGA-WZ strapdown airborne gravimeter in Greenland, in an area with good gravity coverage from earlier marine and airborne surveys. An overview of this new system SGA-WZ is given, including system design, sensor performance and data processing. The processing of the SGA-WZ includes a 160 s length finite impulse response filter, corresponding to a spatial resolution of 6 km. For the primary repeated line, a mean r.m.s. deviation of the differences was less than 1.5 mGal, with the error estimate confirmed from ground truth data. This implies that the SGA-WZ could meet standard geophysical survey requirements at the 1 mGal level.

Airborne gravimetry data sparse reconstruction via L1-norm convex quadratic programming

In practice, airborne gravimetry is a sub-Nyquist sampling method because of the restrictions imposed by national boundaries, financial cost, and database size. In this study, we analyze the sparsity of airborne gravimetry data by using the discrete Fourier transform and propose a reconstruction method based on the theory of compressed sensing for large-scale gravity anomaly data. Consequently, the reconstruction of the gravity anomaly data is transformed to a L1-norm convex quadratic programming problem. We combine the preconditioned conjugate gradient algorithm (PCG) and the improved interior-point method (IPM) to solve the convex quadratic programming problem. Furthermore, a flight test was carried out with the homegrown strapdown airborne gravimeter SGA-WZ. Subsequently, we reconstructed the gravity anomaly data of the flight test, and then, we compared the proposed method with the linear interpolation method, which is commonly used in airborne gravimetry. The test results show that the PCG-IPM algorithm can be used to reconstruct large-scale gravity anomaly data with higher accuracy and more effectiveness than the linear interpolation method.

Gravity Anomaly Data Reconstruction Based on Improved Interior Point Method in Airborne Gravimetry

Strap-down air borne gravimeter is the core sensor of strap-down gravimetry system. In this paper, A new strap-down airborne gravimeter called SGA-WZ has been developed by the Laboratory of Inertial Technology of the National University of Defense Technology. Precise gravity anomaly data reconstruction is the key technology in airborne gravimetry based on the SGA-WZ. This paper explores a method for large scale precise gravity anomaly data reconstruction using the theory of Compressed Sensing (CS). Based on the CS theory, the gravity anomaly data reconstruction can be transformed into the one-norm convex quadratic program to be solved by several methods such as interior point methods (IPM). This paper presents an improved IPM for performing the large scale gravity anomaly data reconstruction precisely that uses the Preconditioned Conjugate Gradients Algorithm (PCG) to compute the search direction. And then, a flight test has been carried out in China with SGA-WZ. The test results have shown that the PCG-IPM algorithm can reconstruct the large scale gravity anomaly data with higher accuracy than the existing nearest interpolation method in airborne gravimetry.

Прогресс в разработке бесплатформенного лазерного аэрогравиметра в Китае

Прогресс в разработке бесплатформенного лазерного аэрогравиметра в Китае

Experimental Investigations on Airborne Gravimetry Based on Compressed Sensing

Gravity surveys are an important research topic in geophysics and geodynamics. This paper investigates a method for high accuracy large scale gravity anomaly data reconstruction. Based on the airborne gravimetry technology, a flight test was carried out in China with the strap-down airborne gravimeter (SGA-WZ) developed by the Laboratory of Inertial Technology of the National University of Defense Technology. Taking into account the sparsity of airborne gravimetry by the discrete Fourier transform (DFT), this paper proposes a method for gravity anomaly data reconstruction using the theory of compressed sensing (CS). The gravity anomaly data reconstruction is an ill-posed inverse problem, which can be transformed into a sparse optimization problem. This paper uses the zero-norm as the objective function and presents a greedy algorithm called Orthogonal Matching Pursuit (OMP) to solve the corresponding minimization problem. The test results have revealed that the compressed sampling rate is approximately 14%, the standard deviation of the reconstruction error by OMP is 0.03 mGal and the signal-to-noise ratio (SNR) is 56.48 dB. In contrast, the standard deviation of the reconstruction error by the existing nearest-interpolation method (NIPM) is 0.15 mGal and the SNR is 42.29 dB. These results have shown that the OMP algorithm can reconstruct the gravity anomaly data with higher accuracy and fewer measurements.

Improving airborne strapdown vector gravimetry using stabilized horizontal components

Abstract Integrating the deflections of the vertical along the flight line can yield geoid profiles which are valuable in the study of geodesy and geophysics, fortunately, the deflections can be measured directly by vector gravimetry. Airborne vector gravimetry using a Strapdown Inertial Navigation System and the Global Navigation Satellite System (SINS/GNSS) has shown promising results in previous studies. However, the quality of the SINS and GNSS is a major limitation; in particular, the attitude errors induced by the gyros will result in large measurement errors to the horizontal components of the gravity disturbance, and these measurement errors represent the behavior of low-frequency trend. An airborne vector gravimetry method used to remove the bias and low-frequency trends in the gravity disturbance estimated for each survey line has been developed. This method uses the horizontal components of the gravity disturbance computed from EGM2008 (Earth Gravitational Model 2008) as a reference. Firstly, the horizontal measurement results obtained from the gravimeter are divided into high- and low-frequency components according to the resolution of the EGM2008, and then, the bias and low-frequency trends of the low-frequency components are corrected using a linear fit to the EGM2008 reference data. Finally, the ultimate results can be acquired after combining the high-frequency components and the corrected low-frequency components. The data used was obtained from the SGA-WZ, which is the first strapdown airborne gravimeter developed in China. The results of this method are promising. The internal accuracy of the gravity disturbance's horizontal components for repeated survey lines exceeds 3.5 mGal, and the corresponding resolution is approximately 4.8 km based on 160-s data smoothing and an airplane averaging speed of approximately 216 km/h. After applying the WCF (Wavenumber Correlation Filter), the internal accuracy of the horizontal components exceeds 2 mGal. This can satisfy the requirement of the application in geodesy and solid earth geophysics.

Long-Term Stability of the SGA-WZ Strapdown Airborne Gravimeter

Accelerometers are one of the most important sensors in a strapdown airborne gravimeter. The accelerometer's drift determines the long-term accuracy of the strapdown inertial navigation system (SINS), which is the primary and most critical component of the strapdown airborne gravimeter. A long-term stability test lasting 104 days was conducted to determine the characteristics of the strapdown airborne gravimeter's long-term drift. This stability test was based on the first set of strapdown airborne gravimeters built in China, the SGA-WZ. The test results reveal a quadratic drift in the strapdown airborne gravimeter data. A drift model was developed using the static data in the two end sections, and then this model was used to correct the test data. After compensating for the drift, the drift effect improved from 70 mGal to 3.46 mGal with a standard deviation of 0.63 mGal. The quadratic curve better reflects the drift's real characteristics. In comparison with other methodologies, modelling the drift as a quadratic curve was shown to be more appropriate. Furthermore, this method allows the drift to be adjusted throughout the course of the entire campaign.

Requirements of Level Arm Measurement Precision in Airborne Gravity

Accelerometer bias and gyro drift determines the long term precision of the strapdown inertial navigation system (SINS) which is the primary and critical component of the strapdown airborne gravimeter (SAG). Making use of the complementary characteristic of DGPS and SINS has been widely and successfully used in many practical applications to prohibit the long term drift on condition that they are consistent in time and space, which stands for time synchronization and lever arm effect respectively. The paper extends kalman filter with lever arm as one of its states and gives the observability analysis in a global perspective. Observability shows that at least two segments of the trajectory with linearly independent angle rate make the lever arm observable. Simulation demonstrates that 10 centimeters error in three quantities of the lever arm vector has an impact at the level of 3 mGal in the horizontal accelerometer bias but little effect on the vertical quantity. Different simulations prove the analysis and highlight the pitch maneuvers during the climbing of the flight test and emphasize the importance of the angle rate to the estimation of the lever arm rather the magnitude of the angle itself.