| CPC G01S 13/955 (2013.01) [G01S 13/86 (2013.01); G01S 13/958 (2013.01)] | 7 Claims |
|
1. A method for retrieving tropospheric wet delay and atmospheric water vapor content over polar sea ice with TDS-1 satellite grazing angle spaceborne GNSS-R, comprising the following steps:
Step 1, obtaining TDS-1 GNSS-R raw intermediate frequency signal data, VMF3 grid data, GPT3 grid data and ERA5 data;
Step 2, correcting an error of a tropospheric wet delay estimation of the grazing angle spaceborne GNSS-R, comprising: preprocessing raw intermediate frequency signals of the TDS-1 satellite by performing closed-loop tracking of direct signals and computing reflected signal carrier phases using an open-loop tracking model; removing dynamic phase components comprises receiver clock deviation, orbit error, ionospheric delay, and carrier phase ambiguity by approximating orbit error through a time-dependent correction function and performing ionospheric delay correction using total electron content information obtained from a global ionospheric map and ionospheric reference model data; reconstructing reflected signal phases by segmenting the residual carrier phase into different frequency components using wavelet transform, mitigating signal discontinuities caused by cycle slips through interpolation, and suppressing phase fluctuations using a filtering process; and correcting residual phase discontinuities by applying a phase unwrapping procedure based on an extended Kalman filter, implemented with a nonlinear signal model configured for in-phase and quadrature data, to produce a continuous and stabilized carrier phase measurement;
Step 3, constructing a grazing angle spaceborne GNSS-R tropospheric wet delay estimation model by combining a grazing angle spaceborne GNSS-R phase measurement theoretical model and a slant tropospheric delay theoretical model considering a mapping function; specifically comprises following sub-steps:
Step 3.1, constructing the grazing angle spaceborne GNSS-R phase measurement theoretical model, wherein an expression is:
ΦR(t)=|rtx(t−ΔtR)−rsp(t)|+|rsp(t)−rtx(t)|+IR(t)+TR(t)btx(t−ΔtR)−brx(t) (9)
wherein rtx, rsp and rrx respectively represent a position vector of a GNSS satellite, a mirror point and a position vector of a TDS-1 satellite in Earth-Centered, Earth-Fixed (ECEF) coordinates, and btx and brx are clock deviations of a GNSS transmitter and a TDS-1 satellite receiver respectively, IR is influence of ionosphere on a carrier phase, and TR is tropospheric delay;
after correcting errors, noises and cycle slips caused by ionospheric propagation, a GNSS satellite orbit and clock error, a TDS-1 orbit and clock error, residual carrier phases are mainly affected by the tropospheric delay in atmosphere, and a tropospheric information measurement equation is expressed as:
TR(t)=ΦR(t)−(|rtx(t−ΔtR)−rsp(t)|+|rsp(t)−rtx(t)|)+btx(t−ΔtR)−brx(t)−IR(t) (10)
wherein ΦR is a reflected signal phase distance;
Step 3.2, estimating GNSS-R slant tropospheric delay by using residual phases of reflected signals:
TR(t)=ΦR(t)−ĝR(t)−ÎR(t)+M(t)λ+ε(t) (11)
wherein Λ represents an estimation of variables in equation (9), ĝR represents geometric and clock components in the equation (9), M represents an unknown integer of a phase ambiguity, and ò represents influence of various estimation errors and noises;
the slant tropospheric delay is modeled as:
 wherein mdry and mwet are mapping functions of dry delay and wet delay in troposphere, ΔLa(e,α) is an error caused by a gradient change of the atmosphere in a horizontal direction, e is a cut-off altitude angle of a satellite, a is an azimuth angle of the satellite,
 and  are obtained by interpolation based on grid data, and then obtaining a following expression: Step 4, calculating grazing angle spaceborne GNSS-R ZWD;
Step 5, calculating a Tm value of a target point based on a GPT3 model, substituting the Tm value into a conversion factor II, and combining calculated GNSS-R ZWD to obtain a GNSS-R IWV estimated value; and
Step 6, verifying inversion performance of GNSS-R ZWD and IWV by using reference data.
|