Questions & Answers
The land deformation measurements available through CATALYST Insights are capable of detecting small movements of the surface. This can often be used to detect and track underground activity, but the detection of movement is on the surface.
Our Insights platform allows you to view the measurements of displacement by both points and fields (area). The measurement fields are derived from the points (persistent scatterers) using an interpolation technique
For many applications you do not need any additional devices installed on earth to get good measurements. However, some locations and applications (e.g. highly vegetated areas) may benefit from the use of corner reflectors.
CATALYST Insights currently supports Sentinel-1 imagery, which goes as far back as 2014. However, we are working with a number of commercial data providers to offer this web-based information using data acquired from their sensors, which date back even further
The ground deformation measurements over California showcased in the demonstration were already processed with our in-house algorithms and workflow. However, CATALYST insights will process new measurements on demand, based on your area, date range, and project criteria.
Yes. The InSAR and Persistent Scatterers workflow were developed by our in-house SAR science team.
We are not using a single reference file, we use a sequential technique that follows the SBAS approach. Each pair in the time series is made up of a reference and dependent image. The pair is co-registered together in order to extract an deformation map of the time period. To create the time series trend, each new reference in a pair is the dependent image from the most recent pair. This ensures that all images are accurately aligned tighter and generates a time series deformation product. “
No, we cannot use imagery from different sensors to create an interferogram, so we cannot use images from different sensors in the same time series. However, we can generate multiple time series, each specific to the sensor and calculate the deformation from each to provide deformation measurements at smaller time intervals.
Not with CATALYST Insights at this time. Our algorithms and workflows are designed and calibrated to work with satellite SAR imagery
This depends on the area and application. In most urban, construction and mining sites were it is easy to find many persistent scatterers, no previous work is required. In more vegetated areas and where specific measurements and precision are required, you may benefit from installing corner reflectors
Spatial Resolution: This depends on the sensor used. For Sentinel-1 the resolution is resampled to about 15m GSD. However, many commercial sensors offer sub meter resolution as high as 50cm.
Temporal Resolution: For Sentinel-1 this is as frequent as 6 days. However, new commercial constellations are being launched that will be able to provide same day measurements, even perhaps hourly measurements.
This would be very tricky and may not yield reliable results. We would recommend corner reflectors be installed to get more reliable persistent scatterers.
The displacement trends for different sampling points were similar was due to the uniform deformation occurring across the area of interest. If non-uniform change occurred,
we would see differences in the displacement trends across the sampling points.
Spaceborne InSAR cannot be use for precise estimation of depth and thickness of various subsurface layers and their relative water yielding capacity or to estimate ground water available resources. The SAR signal in the C-band (5.6cm) cannot penetrate the surface for more than a few cm when the soil layer is dry and compose of lossy material.
Spaceborne InSAR can be used to predict and monitor the consequence of aquifer depletion such as land subsidence.
Measuring building height changes is possible with InSAR technique but we recommend commercial SAR imagery with a high spatial resolution
The mm accuracy is in theory possible and can be sometimes verified using a corner reflector or a well-defined permanent scatterer (i.e.. phase center always at the same position) monitored with precise GNSS measurements. In reality, InSAR data need to be average to reduce the impact of different noise terms and signal decorrelation plus some statistical estimation of the surface movements when computing the surface deformations. The mm accuracy is what is possible to achieve but the accuracy of some persistent scatterers can be in the cm range. This is why it is necessary to use large stacks of data of at least 15-20 images for PSI.
Yes and no. Earthquake are catastrophic events (i.e. they happed suddenly) that are very hard to predict despite 50 years of research. Using InSAR technique, you can observed gradual terrain deformations (subsidence or uplifting) before the Earthquake but you cannot predict precisely when the earthquake will happened by extrapolating the trends. This paper published in 2017
gives and excellent overview of the problematic, especially the figure 1.
It would be recommended to install corner reflectors in areas that are not obstructed by the trees.
The changes are relative from the line of light (LOS) which contains both horizontal and vertical movements that cannot be separated. Using two stacks of data, one ascending and one descending, it’s possible to convert LOS movement to a 3D geodetic coordinate.
We have implemented a proprietary hybrid PSI workflow that correspond to the industry standard without relying on open-source code. We use a combination of SBAS and techniques similar to Stamps
Not with typical InSAR methodology, the phase decorrelation over vegetated areas is too high. Could be possible with (stereo) radargrammetry.
Yes, but there are limitations if 1) the slope is heavily vegetated and/or 2) the slope is too steep and exceeds the ambiguity height.
The accuracy is good for regional studies due to Sentinel-1’s medium spatial resolution. However, monitoring, for example, a small dam would require a finer spatial resolution.