Design Bistatic Interferometric DEM Generation Algorithm and Its Theoretical Accuracy Analysis for LuTan-1 Satellites

doi:10.11947/j.JGGS.2022.0104

Abstract

Abstract:

LuTan-1 (LT-1) is a constellation with two full-polarization L-band radar satellites designed by China, and the first satellite was scheduled to be launched in December 2021 and the second one in January 2022. The LT-1 will be operated for deformation monitoring in repeat-pass mode, and for DEM generation in bistatic mode, improving self-sufficiency of SAR data for the field of geology, earthquake, disaster reduction, geomatics, forestry and so on. In this paper, we focused on designing an algorithm for interferometric DEM generation using LT-1 bistatic satellites. The basic principle, main error sources and errors control of the DEM generation algorithm of LT-1 were systematically analyzed. The experiment results demonstrated that: ① The implemented algorithm had rigorous resolution with a theoretic accuracy better than 0.03m for DEM generation. ② The errors in satellite velocity and Doppler centroid had no obvious effect on DEM accuracy and they could be neglected. While the errors in position, baseline, slant range and interferometric phase had a significant effect on DEM accuracy. And the DEM error caused by baseline error was dominated, followed by the slant range error, interferometric phase error and satellite position error. ③ To obtain an expected DEM accuracy of 2m, the baseline error must be strictly controlled and its accuracy shall be 1.0mm or better for Cross-Track and Normal-Direction component, respectively. And the slant range error and interferometric phase error shall be reasonably controlled. The research results were of great significance for accurately grasping the accuracy of LT-1 data products and their errors control, and could provide a scientific auxiliary basis for LT-1 in promoting global SAR technology progress and the generation of high-precision basic geographic data.

Key words: Synthetic Aperture Radar; bistatic InSAR; LuTan-1; Digital Elevation Model (DEM); baseline error

Bing XU,Liqun LIU,Zhiwei LI,Yan ZHU,Jingxin HOU,Wenxiang MAO. Design Bistatic Interferometric DEM Generation Algorithm and Its Theoretical Accuracy Analysis for LuTan-1 Satellites[J]. Journal of Geodesy and Geoinformation Science, 2022, 5(1): 25-38.

Figures/Tables 12

Fig.1

Tab.1

Pseudo-code of algorithm implementation"

S 1 ?

and

V 1 ?

is the master satellite’s position and velocity, and they shall be computed for each row. */
/*R₁ is the master satellite’s slant range and it shall be computed for each column. Doppler centroid f_d is computed from the doppler polynomial. */
/*Φ is the two-dimensional unwrapped interferometric phases, which consists of flat-earth and topographic phase components. */
/* LON, LAT, HEI are longitude, latitude and height matrix to store the geodetic coordinates, and they have same dimension of Φ. */
1 Begin
2 Read unwrapped phase Φ and SAR geometry parameters
3 for each row do
4 compute

S 1 ?

and

V 1 ?

, and construct R_tcn
5 compute baseline

B ? tcn

and compute

B ? = R T tcn · B ? tcn

6 construct R_vpq
7 For each column do
8 compute slant range R₁ and doppler centroid f_d
9 Get phase φ at Φ and compute ΔR with Eq. (10)
10 compute

L ? 0

(Eq.(12)) and determine

l ? 0, vpq

(Eq.(13))
11 compute l_v with Eq. (7)
12 compute l_p with Eqs. (8) and (9)
13 compute l_q with Eqs. (11) and (14)
14 compute

P ?

with Eq. (6)
15 compute

P ? geo

with Eqs. (15)—(17)
16 save

P ? geo

to LON, LAT and HEI matrix
17 end
18 End
19 Write LON, LAT and HEI results to file
20 End

Tab.1

Tab.2

Fig.2

Fig.3

Fig.4

Fig.5

Tab.3

Tab.4

Fig.A1

Fig.A2

Fig.A3

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Parameter	Value
Master satellite position	S_x=-1823415.5m, S_y=4947197.6m, S_z=4435945.3m
Master satellite velocity	V_x=3242.1m/s, V_y=-3957.4m/s, V_z=5729.7m/s
Slave satellite position	S_x=-1822928.1m, S_y=4947067.2m, S_z=4435702.2m
Radar wavelength	λ=0.236m
Image time	Start time t₀=65493.87s, Center time t_c=65497.29s, End time t₁=65500.71s
Baseline initial value in TCN	B_t_,0=0.0m, B_c_,0=-401.6440m, B_n_,0=379.0245m
Baseline velocity value in TCN	α_t=0.0m, α_c=0.42970m/s, α_n=-0.03478m/s
Range	R₁=713436.279m, R₂=713421.289m
Doppler centroid	f_d=16.38Hz

Errors	Factor k	Correlation R²	Error led to Δh=2m
ΔS_x	0.3269	0.9912	ΔS_x=6.118m
ΔS_y	0.6788	0.9998	ΔS_y=2.946m
ΔS_z	0.6581	0.9785	ΔS_z=3.039m
ΔV_x	0.0	0.9692	/
ΔV_y	0.0	0.9942	/
ΔV_z	0.0	0.9703	/
ΔB_c_,0	505.2	0.9997	ΔB_c_,0=0.0040m
ΔB_n_,0	592.6	0.9996	ΔB_n_,0=0.0034m
Δα_c	505.3	0.9996	Δα_c=0.0040m/s
Δα_n	592.5	0.9997	Δα_n=0.0034m/s
ΔR₁	0.7025	0.9962	ΔR₁=2.847m
Δφ	0.0798	0.9885	Δφ=25.06°
Δf_d	0.0036	0.9932	Δf_d=555.56Hz