slide 60

This presentation discusses the use of interferon grids for time series analysis in SAR. It explains the difference between persistent scatterers and distributed scatterers and how they provide reflective signals. Two types of time series techniques are introduced: PS-InSAR for persistent scatterers and SBS for distributed scatterers. The reason for focusing on distributed scatterers is to extract useful information and reduce noise through increased measurements. In the following slides, I'm going to introduce you how to use many interferon grids to do time series analysis. The term time series in SARs is actually time series in SAR. But in SAR literature usually says time series in SAR. Before talking about time series techniques, I would like to first talk about the properties of the scatterers. In general, we can categorize scatterers into two groups. Persistent scatterers and distributed scatterers. Persistent scatterers means their surface properties do not change over time. So if a pixel has persistent scatterers, the pixel can provide strong and stable reflective signals. You can see the left figure. Main buildings and bedrock are considered persistent scatterers. Unlike persistent scatterers, the surface properties of distributed scatterers change rapidly in time. So a pixel having distributed scatterers cannot provide strong and stable reflective signals. The examples of distributed scatterers include the bare soil and agricultural field. Now, there are two types of time series techniques that target pixels having persistent scatterers and distributed scatterers respectively. Persistent scatterers in SAR, PS-InSAR, focuses on the pixels having persistent scatterers. Small bedrock in SAR, SBS, focuses on distributed scatterers. It makes sense that PS-InSAR only monitors persistent scatterers because they can provide reliable measurements. But why SBS wants to focus on distributed scatterers? Actually, distributed scatterers still include useful information. To reduce the noise, one of the approaches is to increase the measurements. So SBS uses many interferons to extract information from noisy measurements.