A radar satellite can measure diastrophism or ground transformation caused by volcanic activity or an earthquake up to a few centimeters by comparing acquired data in the same area at different times. For example, the location of a magma reservoir and its movement from surface displacement can be estimated by continuously monitoring volcanoes, and such an estimation can contribute to understanding volcanic activities. Data to be acquired by ALOS-4 will also be used for comparison with data acquired by DAICHI-2, which flies on the same orbit, to investigate changes.
If DAICHI-2 tries to cover all active volcanoes in Japan, it can observe one volcano just four times a year, hence more frequent observations would be performed only if a certain volcanic activity gets more active. ALOS-4 will increase the observation frequency to once every two weeks so that disaster prevention agencies can find abnormal changes such as unusual volcanic activity, land subsidence, or landslides at an early stage to timely warn people nearby. In addition, the observation swath will be drastically increased from 50 km to 200 km while keeping the high resolution, as you can see in Figure 1. Therefore, we can observe a broader area at the same time when a large-scale disaster that damages wide areas occurs, such as a huge earthquake or multiple eruptions at the same time.

Forest covers 30 percent of the all land area in the world, and deforestation is strongly related to the increase of greenhouse gases. Therefore, forest conservation and assessment are important. JAXA and the Japan International Cooperation Agency (JICA) are cooperatively developing the JICA-JAXA Forest Early Warning System in the Tropics (JJ-FAST). Using observation data by DAICHI-2, the JJ-FAST can detect areas of deforestation in the order of a few hectares in 77 countries. However, there are many smaller deforestation areas, hence we receive requests for more detailed and frequent observations. The ALOS-4 will conduct observations more frequently with five times more precision to detect smaller deforestation areas that cannot be monitored by DAICHI-2.