Instantaneous velocity determination and positioning using Doppler shift from a LEO constellation

To provide backup and supplementation for the Global Navigation Satellite System(GNSS),Doppler shift from Low Earth Orbit(LEO)satellites can be used as signals of opportunity to provide positioning,navigation,and timing service.In this contribution,we frst investigate the model and performance of instantaneous velocity determination and positioning with LEO satellites.Given a LEO constellation with 288 satellites,we simulate Doppler shift observations at nine multi-GNSS experiment stations.Owing to the lower orbit,the performance of LEO velocity determination is much more sensitive to the initial receiver position error than that of GNSS.Statistical results show that with the initial receiver position error increased from 0.1 to 10 m,the Root Mean Square Errors(RMSEs)increase from 0.73 to 2.65 cm/s,0.68 to 2.96 cm/s,and 1.67 to 4.15 cm/s in the east,north,and up directions,respectively.The performances with GPS are compared with GPS+LEO,and it is found that LEO Doppler shift observations contribute to GPS velocity determination.As for LEO Doppler positioning,even if more than 30 visible LEO satellites are available,the position dilution of precision values can reach several hundreds.Assuming that the error of LEO Doppler measurements is 0.01 m/s,the instantaneous Doppler positioning accuracy can achieve about a few meters,which is comparable to that of GNSS pseudorange positioning.A constant velocity model is adopted for state transition.Static LEO Doppler positioning results show that an accuracy at centimeter to decimeter level can be achieved after solution convergence.For a static simulated kinematic positioning test,the RMSEs range from a few decimeters to several meters in diferent regions by giving diferent constraints.For a dynamic positioning test,the RMSEs are about 2–3 m in high latitude region.

ISAR Imaging and Cross-Range Scaling Based on Image Rotation Correlation

With the rapid advancement of technology,not only do we need to acquire a clear in-verse synthetic aperture radar(ISAR)image,but also the real size of the target on the imaging plane,so it’s particularly important for the ISAR to rescale the images.That is,the ISAR image which is in the range-Doppler domain is converted into the range-azimuth domain.Actually,the key point to solving the problem is to estimate the rotation parameters.In this paper,a new scheme to rescale the images is proposed.For the sake of solving the problem of two-dimensional image blur and target high-speed,the instantaneous range instantaneous Doppler(IRID)method is used to obtain ISAR images,and the rotation parameters are estimated by comparing the rotation correlation of the two images.Using this method,the error of the estimated rotation parameters is greatly reduced,so that the target can be rescaled accurately.The simulation results verify the ef-fectiveness of the proposed algorithm.

Unparallel trajectory bistatic spotlight SAR imaging

A new approach for unparallel trajectory bistatic spotlight SAR imaging is proposed. The approach utilizes the concept of instantaneous Doppler wavenumber and introduces two variants, the sum-range and subtraction-range, to develop the 2D frequency analytical formula. Based on the assumption of plane wavefront, the transmitting and receiving Doppler are separated and formulated via series reversion. And frequency scaling is applied to focus image. The algorithm is with high computational efficiency, and provides well focus for limited scene imaging. Simulation result confirms the validity of the approach.