RTC On Demand!

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Select an area on the map manually using the Area Of Interest map tools. You can choose to draw a point, line, square, polygon, or circle on the map, and edit or delete your drawing.

OR

Expand the Area of Interest section to import a shapefile, GeoJSON, or KML file. Drag and drop a file, or click the Import File button to browse to a file location.

For un-projected shapefiles (in a Geographic Coordinate System using latitude/longitude in degrees), only the file with the .shp extension is required. If the shapefile is in a projected coordinate system (UTM, State Plane, Web Mercator, etc.), zip all the component files together and import the zip file.

You can also narrow your search results by date range, file type, and other parameters.

You can process either GRD or SLC products to RTC, so consider setting your file type search to one or the other to reduce the number of results.

The GRD files have browse images, while SLCs do not. If you want previews of the images in your search results, include GRDs in your file type selection.

Click on a scene of interest in the results (left panel). The footprint will be outlined in red on the map. Files associated with the scene are listed in the right panel.

Alternatively, click on a footprint in the map to highlight a product with that footprint in the results list.

Click on the Zoom icon next to an item in the results list to zoom to the extent of that item in the map.

Click the Zoom icon at the top of the list to zoom to the extent of all the results in the list.

If you find a footprint that covers your area of interest well, click the More Like This button to filter the results to include only acquisitions with that same path and frame.

This button adds the Path and Frame numbers of the selected image to the Search Filters. To remove this restriction, click the Filters button, scroll to the Path and Frame section at the bottom, and click the Clear button.

To add a scene to the processing queue, click the On-Demand icon displayed next to valid file types (GRD or SLC) and select Add RTC GAMMA to On Demand.

The icon appears both in the results list on the left and the file list pane on the right; you can use either one.

Set Processing Options as desired. In Vertex, hover over each option for a brief description. Refer to the  Processing Options and Optional Files  section in ASF's  RTC Product Guide  for more information about the options. When in doubt, leave them set to the default values.

Continue scrolling to learn more about the processing options available, or skip to the  Submit Jobs  section to continue the process of ordering On Demand products.

The Radiometry option allows users to set their preferred backscatter coefficient normalization to either gamma-nought (gamma-0 or γ ₀ ) or sigma-nought (sigma-0 or σ ₀ ) radiometry.

Gamma-0 is normalized by the illuminated area projected into the look direction (A _γ  - the yellow area with the red outline in the diagram) and sigma-0 is normalized by the ground area (A _σ  - the grey area with the purple outline in the diagram).

Diagram from David Small, Flattening Gamma: Radiometric Terrain Correction for SAR Imagery, IEEE Transactions on Geoscience and Remote Sensing, vol. 49, no. 8, August 2011.

For most GIS applications, or analyses where the impact of topography is of interest, gamma-nought is preferred.

Refer to the  Radiometry section in ASF's Sentinel-1 RTC Product Guide  for more information on this option.

The Scale option allows users to choose the scale of the output backscatter images from the three commonly used scales for calibrated SAR values: power, amplitude, or decibel (dB).

The  Scale Conversion Tool tutorial  provides additional guidance on visualizing and converting RTC products from one scale to another.

The default output of Sentinel-1 RTC products is power scale. The values in this scale are generally very close to zero, so the dynamic range of the RTC image can be easily skewed by a few bright scatterers in the image.

Power scale is appropriate for statistical analysis of the RTC dataset, but is probably not the best option for data visualization.

Adjustments can be made to the stretch settings when viewing the raster in a GIS environment, but other scales will require less adjustment, and will render better as stand-alone images.

Values in the amplitude scale are the square root of the power scale values. This brightens the darker pixels (values less than 1) and darkens the brighter pixels (values greater than 1), narrowing the dynamic range of the image.

In many cases, amplitude scale presents a pleasing grayscale display of RTC images without having to make any stretch adjustments.

Amplitude scale also works well for a range of statistical analyses, including calculating log difference ratios, as described in the  Log Difference Tool tutorial .

The decibel (dB) scale values are calculated by multiplying the log of the power scale values by 10: dB = 10 x log10(power)

This scale allows for greater differentiation among very dark pixels.

This is often a good scale to use for identifying water on the landscape; the water pixels generally remain very dark compared to the much brighter pixels of the surrounding landscape.

Because dB is a logarithmic scale, it may not be appropriate for some types of statistical analyses. It can also result in poor differentiation among terrestrial features, or a "washed-out" appearance.

The  Reclassify RTC Tool tutorial  uses the dB scale to classify surface water and generate a water mask.

Explore the map. Pan and zoom, and click on pixels to compare the values from the different scales.

Refer to the  SAR Scale section in ASF's Sentinel-1 RTC Product Guide  for more information on the different scales.

The Pixel Spacing parameter sets the pixel size of the output images. Users have the option to set the pixel spacing of the output products to be 30, 20, or 10 meters.

• The 30-m product has the smallest file size. In most cases, this pixel spacing matches the native resolution of the DEM used for RTC processing.
• The 10-m product provides much more detail of surface features, and it is closer to the native resolution of the source Sentinel-1 data. The 10-m products are almost ten times as large as 30-m products, so they take much longer to process, download and analyze.
• The 20-m product may be a good compromise between the native resolution of the source SAR imagery and the source DEM, and the file size is about twice the size of a 30-m product, making it much easier to work with than a 10-m product.

Look at the illustration showing images of products generated with different pixel spacing, and compare the level of detail available in each. Some features, such as significant waterways, are clearly visible in the 10-m product. These features are also visible in the 20-m product, though to a lesser extent, but they cannot be detected in the 30-m product.

It is much faster to process, download, and analyze 30-m RTC products, which have significantly smaller file sizes than the 10-m products. If they do not provide sufficient detail for your use case, however, try the 20- or 10-meter RTC products.

Consider the size of the RTC VV GeoTIFF file for each of the images included in this comparison:

• 30-m: 267 MB
• 20-m: 600 MB
• 10-m: 2350 MB

The 20-m product is often a good compromise between resolution and file size. The amount of detail is much closer to the 10-m product than the 30-m product, but the file size is much closer to the 30-m product than the 10-m product.

Refer to the  Pixel Spacing section in ASF's Sentinel-1 RTC Product Guide  for more information.

The DEM Matching option allows users to either try to coregister the SAR image to the DEM file, or simply use the Sentinel-1 orbit files for geocoding the RTC products.

Check the DEM Matching box in the Apply section to attempt coregistration of the SAR image to the DEM file. Leave the check box blank to use the Sentinel-1 orbit files.

Applying the DEM Matching option can improve the quality of the RTC calculations, as the features in the SAR image are matched to the features in the DEM, minimizing the offsets in geometry during the backscatter normalization calculations.

If, however, the georeferencing of the DEM doesn't match the georeferencing of the Sentinel-1 imagery, or in areas that lack distinctive topographic features, DEM matching can result in variable offsets in the output images from one Sentinel-1 acquisition to the next. This makes it more difficult to overlay images for time series analysis.

• If you are interested in optimizing the RTC calculations, and are less concerned about consistent geolocation through time, the DEM Matching option is likely a good choice.
• In cases where consistency is more important than accuracy, consider not applying DEM Matching, or at least testing the feature alignment of the output products to make sure they are suitable for your application.

Refer to the  DEM Matching section in ASF's Sentinel-1 RTC Product Guide  for more information.

When the box is checked to apply the Speckle Filter option, an Enhanced Lee filter is applied during RTC processing to remove speckle while preserving edges of features.

Speckle occurs due to interference among signal waves, as they interact with different scatterers on the surface of the earth and return to the sensor. It appears as granular noise in the image.

Applying a speckle filter can smooth the appearance of the image, but it comes at a cost to the resolution of the output RTC product. 

Use the slider to compare an RTC product without the speckle filter option applied (on the left) to the same product with the speckle filter option applied (on the right).

We do not currently offer any customization options for the speckle filter. It may not be appropriate for all use cases, so evaluate some test images first to determine if the results are better suited to your application with or without the speckle filter.

Refer to the  Speckle Filter section in ASF's Sentinel-1 RTC Product Guide  for more information.

There are a number of ancillary files produced during RTC processing that are not included in the RTC product package by default, but may be of interest to some users.

In the On Demand queue, the optional files are listed in the Include section. Check the box(es) next to the files that you want to include in the product package.

These files increase the size of the product package; excluding them reduces the download size for those who do not need or want them.

Scroll down to learn more about each of the optional files.

Type in a Project Name, or choose from a list of previously used names. The list appears when you click in the Project Name field.

Click the Submit Jobs button to start processing.

When products are queued, they are listed as Pending. When processing begins, the status changes to Running.

Once processing is complete, a zip file is listed, and the product is available for download. 

Filter your On Demand products by Project Name (type in or select from dropdown) or acquisition Start/End Date.

Click the Filters button for more options. You can search for any part of the filename using the Product/Source Scene field, or filter by Job Status (Pending, Running, Succeeded).

Once products are complete, they are available to download for 14 days. After 14 days, products are still listed, but marked as Expired and no longer available for download.

You can hide/show expired products in the results list by clicking the Expired button.

• To process an expired job again using the same processing parameters as before, click the Expired button and select Resubmit Job. This is handy if you forgot to download your product before it expired.
• To process the same source scene with different processing parameters, click the On Demand icon to add the source scene to the On Demand Queue, where you can set new processing options.

To download completed products one at a time, click the download icon (on the left in the icon pair displayed in the right panel).

To add a product to the Download Queue, click the cart icon (either in the results list in the left panel or the file list in the right panel).

Click the Queue button at the top of your results list to add all of the listed products to your Downloads queue.

Click on the Downloads button to open the Downloads queue.

Use the icons next an item to either download it individually in your browser or remove it from the queue.

The Download All option will work best for most users. It uses the multi-threading capabilities of your browser to download several items at a time until all items in the queue are downloaded.

Other options:

1. Download Python Script will download a script. Run it to download all of the files in your Downloads Queue sequentially. You must have Python installed on your computer to use this option.
2. The Copy URLs button copies a list of the download URLs for the items in your queue, which you can paste into your own download script.