Introduction to Umbra's SAR Data
Umbra's satellites produce X-band synthetic aperture radar data which can be dissected into two constituent properties: amplitude and phase.
Phase ("Complex Product")
Image Formation (Polar Format Algorithm)
Amplitude ("Detected Product")
The strength of a signal returning to the antennae is defined by its amplitude. The greater the amplitude, the stronger the signal (resulting in a "brighter" appearance when visualized as a grayscale image). SAR is most commonly visualized according to its amplitude.
The characteristic black-and-white images commonly associated with SAR are amplitude products. Amplitude data can be used for mapping features on the ground, measuring surface roughness, or even basic change detection.
Phase ("Complex Product")
Phase information is determined by the distance from the satellite to the reflecting surface. It can be used to support "range finding" techniques, especially in the context of interferometry (InSAR).
Image Formation
Raw data coming off the satellite is "pre-processed" into more easily interpretable products like the ones described in our File Formats & Standards guide. The least processed form of data Umbra provides is Compensated Phase History Data (CPHD). From there, data is further processed into an "image" using the polar format algorithm and comes in two varieties: detected and complex data.
Image Formation (Polar Format Algorithm)
After compensating for the effects of motion at the CPHD stage, we use a well-known algorithm called the Polar Format Algorithm (PFA) to further refine data into complex phase information (SICD) and amplitude data (GeoTIFF).
The PFA is particularly well suited to agile SAR systems like ours, which can "squint," meaning look slightly forwards or backwards along our flight path (as opposed to staying fixed 90º off the flight path on either side). PFA can handle the complex geometries that arise from "squinted" data.
The PFA is particularly well suited to agile SAR systems like ours, which can "squint," meaning look slightly forwards or backwards along our flight path (as opposed to staying fixed 90º off the flight path on either side). PFA can handle the complex geometries that arise from "squinted" data.
For detailed explanations of Umbra's imaging modes and data formats review these guides elsewhere in the help center in the Imaging Modes section.