Skip to content

PRODUCT FORMATS

Geocoding Information in ICEYE Images

To enable easy and fast geolocation, a processed form of the geometry model called rational polynomial coefficients (RPCs) is provided for each image. RPCs link image locations to ground locations via simple equations that enable rapid calculations. In addition to ease and speed, RPC coefficients have the further advantage of being sensor independent. The structure of the RPC equations is always the same. For this reason, RPC exploitation code does not have to change to accommodate different sensors. In fact, both optical and SAR sensors are modeled by the same RPC structure. Exploitation code that performs geolocation for images from optical sensors can actually be used to derive ground locations from the RPC data included with ICEYE complex and amplitude images. This process is now commonplace in most geospatial viewers (we recommend using QGIS1 and it is freely available for analysts and software developers.)

Info

Image geolocation of any mono image, optical or SAR, requires that an elevation model be used during exploitation. This is true for the physics-based equations and RPCs.

Single Look Complex (SLC) Product

These are full-resolution, single-look images of the focused SAR signals. Scenes are stored in the satellite’s native image acquisition geometry, which is the slant-range-by-azimuth imaging plane. As shown in the green surface in Figure ??, the pixels are aligned perpendicular to the sensor flight track (The pixels have zero-Doppler SAR coordinates}). They are spaced equidistant in azimuth and in slant range. Each pixel contains both amplitude and phase information as represented by a complex magnitude value with in-phase and quadrature components (I & Q).

placeholder

Figure 2: Slant range and ground range image geometry

SLC products are suitable for applications that rely on phase information or require the full image resolution. Because SLC images are in the native sensor orientation, there are no radiometric artefacts induced by the spatial resampling applied to map projection images. The range-azimuth orientation also enables further geometric manipulation, like orthorectification. Ortho versions can be produced using both commercial and free software tools, such as the European’s Space Agency’s Sentinel Application Platform (ESA SNAP S1TBX2).

The SLC product is particularly useful for those analysts who require multiple collections with matching phase data for applications like Coherent Change Detection (CCD). SLC images are typically used by scientists and organisations with advanced SAR expertise, but complex images will become core products for numerous users once SAR applications become more user-friendly.

Amplitude Image

Note

When mapping an image from the slant plane to the ground, the average elevation of the scene is applied to the ellipsoid used in the projection.

These are viewable forms of SAR data used for analyst exploitation; the pixels have brightness values but no phase data. Amplitude images are multi-looked to reduce the salt-and-pepper effect of speckle. The images are also projected from the slant plane onto an ellipsoid model of the ground surface (See Figure 2). The resulting product has approximately square spatial resolution and equal pixel spacing. It also has reduced speckle, due to the multi-look processing. Figure 3 illustrates slant range and ground range projections of amplitude pixels. The pixel's dimensions are equal in range and azimuth in the ground projection on the right.

As with SLC images, sensor-oriented amplitude images maintain the native sensor geometry of range and azimuth and no image rotation to a map coordinate system has been performed. This avoids interpolation artefacts and it supports image stacking for change detection applications and physics-based, rigorous geolocation. ICEYE images can be viewed using open standard GIS readers such as QGIS1.

We do not orthorectify our amplitude images or project them to an ellipsoid-based map projection, but we provide information, which can be quickly applied by users to their ICEYE imagery using freeware software, available on the market. This lowers the cost to our customers and ensures that they are always aware of the provenance of the elevation data used to project the image pixels to the topographic surface. This software is described in our Imagery Product Format Specification Document3.

placeholder

Figure 3: Slant range and ground range images

ICEYE Image Formats

ICEYE SLC products are stored and delivered in the HDF5 format, which is particularly suitable for storing binary complex SAR data channels and annotated metadata. Amplitude images are produced as GeoTiff files. These are readable by common GIS software tools. Additionally, both SLC and Amplitude products are accompanied by XML metadata files. This enables quick screening of products without the use of specialized software. A detailed description of the format of SLC data and amplitude images is given in the ICEYE Product Format Specification Document, which is available on the ICEYE website3.

Complex Amplitude Quicklook
Strip HDF5,XML GeoTiff,XML PNG,KML
Spot HDF5,XML GeoTiff,XML PNG,KML
Scan - GeoTiff,XML PNG,KML

References

  1. QGIS - A Free and Open Geographic Information System. \url https://qgis.org/en/site/. Accessed 2020 Dec 17. ↩↩

  2. European Space Agency. The sentinel application platform - snap. \url http://step.esa.int/main/toolboxes/snap/. Accessed 2020 Dec 17. ↩

  3. ICEYE Level 1 Product Format Specification Document. \url https://www.iceye.com/sar-data/documents/. ↩↩