[feat/ortho] First draft

docs/comingsoon.md

@@ -11,8 +11,5 @@ You have probably seen the video. Because ICEYE satellites can stare at a point
 ### Color Multilook Extended Dwell Imaging
 This is related to SAR Video as it uses the satellite's agility to collect an image over a wide range of angles. We noticed that some objects are more visible when observed from certain directions. The color multilook image may present more options to detect subtle objects in SAR imagery like powerlines or moving targets.
 
-### Orthorectified imagery
-This is a tricky one for ICEYE. We hate the way that orthorectified imagery warps and distorts our beautiful imagery and as SAR professionals we prefer to use GIS tools to correct for SAR layover and geometric distortions. But we have come to realise that there are still a lot of people out there that just want to buy a map-like product. So we are going to do our best to provide it.
-
 ### Access to Phase History Data
 At ICEYE we want to demystify SAR and encourage people to learn about signal processing and make their own SAR images from our data. We think that a good way to do this is to provide raw radar pulse data in a standardised way (eg the NGA CPHD format) so that others can use our received RF signal. Its very niche but may be new developments and applications will come from it thereby making SAR more useful and accessible.

docs/productFormats/grd.md

@@ -71,4 +71,4 @@ Figure 2 provides a useful summary of Amplitude images in the context of the pro
 </figure>
 
 ## References
-\bibliography
+\bibliography

docs/productFormats/ortho.md

@@ -0,0 +1,19 @@
+# The ORTHO product 
+
+Because of the way we acquire and process our data, the amplitude image from raw SLC data appears completely distorted. GIS application require correct "location" of our pixels in order to do precise measurements. We account for three components to these distortions: the aquisition geometry, the curvature of the earth and the local toplogy. Hence the necessity for an orthorectified product. 
+
+## What is Orthorectification?
+
+Orthorectification is the process of compensating for three component of distortion. We will have to calculate how much we "move" our pixels in order to correct for thoses. 
+First, a correction of the distrotions caused by the sensor/scene geometry. SAR satellites observe their target broadside at an angle which cause a 'tilt' and 'strech' of the iamge when layed on a surface representing the earth's surface, for example. Pixels are moved to so called horizontal coordinates, simply at the correct lattitude and longitude coordinates in WGS84 referencial. Our [GRD product](grd.md) already correct for the satellite geometry and the horizontal positions in WGS84 coordinates, remain the earth curvature and the local topology.
+Second we have to account for the global datum of the earth which is mathematically modeled. We evaluation the elevation from the ellipsoid surface model (here EGM16, in WGS84) for each pixels.
+Finally we evaluated add the local elevation from a Digital Evelation Model (DEM). Accuracy of the DEM data is an important factor to properly interpolate the pixels positions.
+The results is a 3D coordinates for each pixels which can be used to project the image plane. 
+
+### DEM
+Currently we can provide orthorectified imagery from the following Digital Elevation models:
+ * Copernicus DEM GLO-30 
+ * Copernicus DEM GLO-90 
+ * NASA DEM version 1
+ * ASTER GDEM version 3
+ Terrain projection is performed with one the chosen DEM using GDAL gdalwarp tool. The new image is stored as a Geotif just like our GRD product. We produce a new XML file from the GRD one with extra field describing the DEM used for orthorectification. 

docs/productFormats/packaging.md

@@ -39,5 +39,5 @@ SAR images can be ordered either from archive (previously collected imagery) or
 
 ICEYE’s focus is currently on the integrity of complex and amplitude images. This will expand over the next year as we introduce a phase history data product and other products derived from complex and amplitude images.
 
-A basic ICEYE product is represented by a set of SAR image binary data, corresponding image metadata and it is delivered as a singular product package. Products are characterized by the payload configuration (such as imaging mode and look direction) used by the respective satellite, as well as the level of processing that has been applied to the SAR scene. With respect to the data geometric projection and representation, products are differentiated into two primary types: geo-referenced Single Look Complex (SLC) and Amplitude Images (Also known as Ground Range Detected (GRD) scenes). SAR image binary data, delivered as digital numbers or quadrature components, can be converted to radar brightness $\beta_0$ and mean radar cross section $\sigma_0$ using the annotated calibration factor in the image metadata.
+A basic ICEYE product is represented by a set of SAR image binary data, corresponding image metadata and it is delivered as a singular product package. Products are characterized by the payload configuration (such as imaging mode and look direction) used by the respective satellite, as well as the level of processing that has been applied to the SAR scene. With respect to the data geometric projection and representation, products are differentiated into two primary types: geo-referenced Single Look Complex (SLC) and Amplitude Images (Also known as Ground Range Detected (GRD) and terrain projected (ORTHO) scenes). SAR image binary data, delivered as digital numbers or quadrature components, can be converted to radar brightness $\beta_0$ and mean radar cross section $\sigma_0$ using the annotated calibration factor in the image metadata.
 

docs/productguide/products.md

@@ -17,12 +17,11 @@ SAR complex images contain pixels that have both amplitude and phase values. The
 
 ### Amplitude Images
 
-These are the familiar SAR gray-scale images with amplitude-only pixels. They are “multi-looked” to reduce the grainy effect of speckle, at the cost of slightly lower resolution. Amplitude images are projected to the ground surface and can be oriented with respect to the sensor or produced on an ellipsoid-based map projection. ICEYE produces amplitude images in the natural range-azimuth sensor orientation because they offer the most flexibility in exploitation. To be consistent with conventional terminology, these sensor-oriented images are called Ground Range Detected (GRD). This term may change in the future to be something more meaningful.
+These are the familiar SAR gray-scale images with amplitude-only pixels. They are “multi-looked” to reduce the grainy effect of speckle, at the cost of slightly lower resolution. Amplitude images are projected to the ground surface and can be oriented with respect to the sensor or produced on an ellipsoid-based map projection. ICEYE produces amplitude images in the natural range-azimuth sensor orientation because they offer the most flexibility in exploitation. To be consistent with conventional terminology, these sensor-oriented images are called Ground Range Detected (GRD). This term may change in the future to be something more meaningful. We also provide terrain corrected amplitude images also called [orthorectified images](../productFormats/ortho.md).
 
 !!! info
     Amplitude images are most useful for rapid observation of a location regardless of lighting or weather conditions.
 
-
 <!-- #### General Phase History Data Product
 ICEYE also produces a basic form of SAR data that contains the raw pulse data before image processing. This data contains phase information as a function of time during the imaging operation and so it is called *phase history data*. This product enables more flexible processing for advanced users who might have their own SAR processor, or who might even prefer to exploit the data before converting it into an image.  -->