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error data, which may used to correct the atmospheric error 
effect of InSAR (Ge, L„ 2001). 
It can be seen that InSAR and GPS data fusion technology can 
break through the limitation of single method and improve the 
resolution both in spatial and temporal. InSAR/GPS fusion 
technique is chosen as an effective means for surface subsi 
dence monitoring in mining area. 
2. GPS/INSAR DATA FUSION THEORIES 
2.1 The processing procedure of InSAR (D-InSAR) data 
used in mining area 
To monitor the mining area’s surface deformation with InSAR 
(D-InSAR), the following strategy could be adopted. 
In the first step, a pair of short time interval (only 1 day) single 
look complex (SLC) SAR imageries should be selected to 
create an interferometric phase image (iph) which reflect the 
DEM of the mining area’s surface, (sometimes <ph could be also 
created with existing DEM and orbital parameters). 
In the second step, select another pair SLCSAR imageries that 
span deformation period and in the same area to create another 
phase image (cps) which includes the information of topographic 
relief. 
In the final step, subtracted (ph from cps, we can get the 
deformation phase image (cpd) and the slant-range changing 
amount (cprd) from microwave transmitter to ground pixels, cprd 
needs to be decomposed into the horizontal and vertical 
displacement components with the baseline parameters and the 
orbit-state vector. 
2.2 Approaches for Improving InSAR data based on GPS 
At present, there are many approaches to improve the InSAR 
data’s quality with GPS technology. Main aspects are as 
follows (Diao, J., 2005): 
1) Atmospheric delay error correction; 
2) Baseline and orbital parameters estimation; 
3) Geometric correction. 
2.2.1 Atmospheric delay error correction 
Atmospheric delay is one of the major error sources in InSAR 
data, which affects the accuracy of mining-induced surface 
subsidence monitoring. Atmospheric delay error includes the 
tropospheric delay and ionospheric delay error. As for dual 
frequency GPS receivers, the pseudo-range measurement 
equation of a certain GPS observation station is shown in 
equation (1) (Chen, J., 2004). 
L\j ~ P j dtrop ^ ion (./l) "f £ 
L 2j = Pj ~ d trop - d ion(fl)+ £ 
where e = other deviation and residual term 
¿¡rap = tropospheric delay error 
dio n {fk) = ionospheric delay error for frequency f k 
2.2.2 Baseline and orbital parameters estimation 
Another error source of repeat-pass InSAR used in monitoring 
the surface deformation in mining area is baseline and orbital 
parameters. In general, baseline can be estimated by using the 
satellites ephemeris parameters. However, the origin motivation 
of sending radar satellite was not for SAR interferometry, it 
caused the ephemeris parameters have lack of accuracy usually 
and cannot meet the demand of SAR interferometry. In order to 
gain high precision baseline vector parameter, ground control 
points (GCP) with high precision can be used to obtain the radar 
satellite baseline vector parameters (Volker, J., et al., 2003). 
This method needs to set equipments that are called comer 
reflectors on the surface of mining area. Figure 1 shows the 
structure figure of comer reflector. 
Comer reflectors can be seen as high bright points in InSAR 
imageries, the interferometric phase differences among these 
points can be exacted according to their phase information. The 
geodetic coordinates and their relative coordinates could be 
gained by GPS measurements. Thus baseline parameters could 
be estimated by using image interferometric phase differences 
and the relative coordinates of ground comer reflectors. 
In order to estimate the InSAR orbital parameters, InSAR 
terrain surveying equation (Shi, S., 2000) must be used. Showed 
in equation (2) and equation (3). 
X' 
a i 
a 2 
a 3 
0 
X" 
Y 
= \ 
b 2 
63 
r sin 9 
+ 
Ys 
Z 
_ c i 
c 2 
c 3 _ 
r cos 9 
. Z s_ 
9 = arccos <f> +a 
2 \ AnB J 
where X, Y,Z = geodetic coordinates of a certain GCP 
a \, a 2, a 3, ■■■C3 = rotation matrix of attitude angles 
X = scale factor 
r = the slant distance from a certain GCP to satellite 
6 = over look angle 
X s , Y s , Z s = orbital position of satellite 
d> =absolute phase of interferometry 
The Satellite orbital attitude parameters and the baseline can be 
expressed by time linear equation or polynomial. Showed in 
equation (4).