MAI (Multiple Aperture Interferometry)

MAI (Multiple Aperture Interferometry) is a technique for measuring ground displacement along flight direction of the satellite (azimuth offset) using two SAR (Synthetic Aperture Radar) images. Whereas a standard InSAR (SAR Interferometry) technique can detect only displacement along line-of-sight (LOS), MAI is capable of measuring displacement along flight direction by applying more elaborated signal processing.
The figure shows a concept of MAI. First, two SAR images with forward and backward looking are generated by applying signal processing to divide a length of a synthetic aperture. Standard InSAR processing is conducted for forward and backward looking images acquired at two different times, resulting in a forward and a backward SAR interferogram. Although both these two interferograms show LOS displacement, the LOS directions are different. By subtracting the backward looking interferogram from the forward looking interferogram, the azimuth offset is detected. The precision of the measurement lower than the standard InSAR, sometimes worsening to a few dozen centimeters.



Illustration of MAI

Advantage

1. An azimuth offset is measurable, which is not detected by InSAR
2. Insensitive to atmospheric noises
3. Large ground displacement is measurable (standard InSAR cannot measure large displacement with a high gradient)

Disadvantage

1. Lower measurement precision than InSAR : sometimes a few dozen centimeters
2. Vulnerable to decorrelation
3. Vulnerable to ionospheric noises