# Validating Precise Orbit Determination from Satellite-Borne GPS Data of Haiyang-2D
###### Abstract
The external validation mainly includes comparison with other technical orbit determination results and SLR range validation. The external methods to validate the accuracy of orbits are more conducive to proving the reliability of the results of LEO POD, but the orbits determined by other techniques are sometimes not obtained in time. In addition, the traditional SLR range validation is also constrained to the number of normal points (NP), and shortcomings of the validation method include failure to clearly show the accuracy of orbits in three-dimensions. Deficiencies in these external validation methods prevent the determined accuracy of satellite orbits from being fully validated on time, affecting the use of altimetry data. Formation satellites such as GRACE and GRACE-FO, K-band ranging (KBR) can be used to validate the accuracy of orbits. It is necessary to perform calculations using the orbit determination results to obtain the relative distance and speed between satellites, and then compare them with the KBR data to evaluate the relative orbit accuracy of the satellites [13; 14; 15]. [PERSON] et al., (2021) proposed verifying the accuracy of the reduced-dynamics (RD) orbits with onboard DORIS data [16]. The quality of satellite data and the orbit determination strategies are the main factors affecting the POD accuracy [17], and the data quality can also be used to evaluate the performance of the receiver [18]. [PERSON] et al., (2010) analyzed the data quality of COSMIC and GRACE regarding the multipath effect, ionospheric delay, cycle slip, etc., then evaluated the performance differences of different receivers. The results proved that high-quality observations are the premise of high-precision orbit determination [19]. [PERSON] et al., (2020) proposed the progressive method to determine orbits without estimating the orbit parameters directly, which reduces the error of matrixes and obtains more reliable orbits [20]. The main aim of this paper is to evaluate the performance of the HY2 receiver and the accuracy of the HY-2D RD orbit. Based on the satellite-borne GPS observations, precise ephemeris, and SLR data, three orbit accuracy assessment methods are proposed to evaluate the accuracy of HY-2D RD orbit: carrier differential validation, inter-satellite differential validation, and SLR three-dimensional (3D) validation. In Section 2, the principle and derivation of three methods of orbit accuracy evaluation are introduced in detail. In Section 3, the data quality of HY-2D collected by the satellite-borne GPS receiver is analyzed with TEQC software regarding the multipath error, cycle slips, and data completeness [21]. The orbit determination strategies are analyzed, and the RD method [22] is used to determine the precise orbits of HY-2D. Carrier-phase residuals are used to evaluate the internal accuracy of POD, and SLR range validation and DORIS validation are used to evaluate the external accuracy. The carrier differential validation, inter-satellite differential validation and SLR 3D validation proposed in this paper are used to evaluate the accuracy of POD, and the reliability of the three methods is verified. Finally, the conclusions are presented.