InSAR technology can acquire high precision digital elevation model (DEM) information, and it is one of the key technologies of SAR topographic mapping. Due to the instability of airborne platform, interferometric parameters of InSAR system are not accurate which have greatly influenced the precision of DEM generation in the process of InSAR. The traditional interferometric calibration method needs many Ground Control Points (GCPs) to reduce the effect of systematic random errors on the calibration precision, but it is very difficult to dispose GCPs in the field with complicated terrains. Therefore, a new calibration method is proposed for airborne InSAR system based on block adjustment theory, the interferometric parameters such as baseline length, baseline angle and absolute time postponement of the airborne InSAR system in different strips can be calibrated by few GCPs.
According to the principle of DEM generation using InSAR, The elevation of ground point P can be expressed as equation (1) in Figure 1, R and R1 are the distances from two antennas to the ground point P, ?R is the slant range difference, B is the baseline length; H is the elevation of the antennas A1; h is the elevation of the ground point P. Equation (2) can be derived from equation(1) as shown in Figure 1.Equation (2) is the calibration model of four interferometric parameters, namely, slant range difference, baseline length, baseline angle, the elevation. This model can be simplified as equation (3) in Figure 1, linearization of equation (3) and error equation can be derived. Figure 2 is the diagram of three-strips block includes GCPs and connect points (CPs), each GCP and CP can generate the error equation. After calculating the normal equation, the accurate interferometric parameters and the elevation of CPs can be solved.
Interferometric parameters calibration is tested with the airborne data acquired in Dengfeng area of China. The experiment area covers flat ground and mountains and other types of terrain features. Experiment has been implemented on four SAR images of two strips and accurate interferometric parameters and the elevation of connect points can be obtained.
As the conclusion, a new calibration method is proposed for airborne InSAR system, the interferometric parameters (baseline length, baseline angle, absolute time postponement, etc) in different strips can be calibrated by few GCPs. A joint calibration experiment using the interferometric data of multi-strips proved the validity and rationality of the proposed method.

Keywords: Airborne interferometric SAR(InSAR); Interferometric calibration; Block adjustment; Vertical control point; Pass point