For the observation by a SAR satellite, the off-nadir angle means the angle between the vertical nadir of the satellite position and the direction of the SAR beam. By adjusting the tilt of the satellite to the right or left, different areas can be observed on the same orbit.
SM1 (GSD 3m / Ultra Fine) is U2-6 to U3-14, SM2 (GSD 6m / High Sensitive) is FP6-3 to FP6-7, SM3 (GSD 10m / Fine) is F2-5 to F2-7. And ScanSAR is assigned a specific beam number for each observation mode such as W2. If you know the beam number, you can specify the observation mode.
The right side obsevation is oftenly adopted for ALOS-2 operation. However, for emergency observations for natural disasters and other applications, the left side observetion is performed.
Figure shows the beam number and off-nadir angle of SM1 observation mode which is suitable for the disaster observation.
In addition to U2 and U3 in the table, beam categories U1 to U5 are available, and the imageries observed in these modes can be purchased. Only beam numbers that have been calibration verified are listed in the table above. The results of the calibration validation can be found here.