Sentinel-1 Burst Extractor
Overview
A Sentinel-1 SLC contains multiple measurement TIFFs that contain the radar response data. Each measurement TIFF can be further broken down into a single radar pulse response message which is referred to as a burst. The Sentinel-1 Burst Extractor allows users to download a single burst from the Sentinel-1 SLC without having to download the entire SLC that contains it.
Definitions
- source zip - A zip file distributed by ASF containing a Sentinel-1 single-look complex (SLC) SAFE archive.
- measurement TIFF - A GeoTIFF (TIFF) file contained within a source zip, which has geocoded radar response data for a single subswath and polarization combination for a given swath.
- burst - A sequence of radar pulses designed to illuminate the same area of Earth's surface on every orbit over that area.
Use Case
GET /{granule}/{subswath}/{polarization}/{burst_index}.{file_type}- Receive HTTP 202 accepted if product has not been generated yet.
- Extraction has begun, wait briefly before submitting step 1 again.
- Receive HTTP 307 with redirect to product if the product has been generated.
Authorization
The Burst Extractor requires a user to authenticate with a NASA Earthdata Login (EDL) account in order to access the data. EDL generates an asf-urs cookie that the extractor API validates. If it is not supplied then a user will be redirected to EDL to authenticate. If the cookie is invalid for whatever reason, e.g. expired, it will respond with an HTTP 403 - Forbidden message.
API Usage
The Burst Extractor host name is sentinel1-burst.asf.alaska.edu.
HTTP request:
GET /{granule}/{subswath}/{polarization}/{burst_index}.{file_type}
API Specification
| Parameter | Type | Value | Description |
|---|---|---|---|
| granule | string | Granule name (i.e., product name) for a level 1 IW or EW SLC as defined at https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/naming-conventions, without the ending '.SAFE'. | Which Sentinel-1 SLC granule to extract a burst product from. The burst extractor uses this value to find the source data in ASF's Sentinel archive. |
| subswath | string | One of 'IW1', 'IW2', 'IW3', 'EW1', 'EW2', 'EW3', 'EW4', or 'EW5'. The mode portion ('IW' or 'EW') must match the mode in the product name. | Subswath of the burst product to retrieve. |
| polarization | string | One of 'HH', 'VV', 'HV', or 'VH'. | Polarization of the burst product to retrieve. |
| burst_index | integer | 0-1499 | Sequence number of the burst data in the source measurement TIFF, starting from 0, in file order (which is acquisition time order). There can be no more than 1500 bursts in a single measurement TIFF per the Sentinel-1 spec. In practice, we've never seen more than 24. |
| file_type | string | One of 'xml' or 'tiff'. | Defines tiff for a burst extraction or xml for a metadata extraction. |
Response Codes
| Code | Content Type | Format | Description |
|---|---|---|---|
| 202 ('accepted') | application/json | {'message':'Accepted'} | Extraction job triggered for the queried product |
| 307 ('temporary redirect') | application/json | {'message':'Temporary Redirect'} | A 307 is returned with the Location header set to the burst product URL if the product exists. |
| 403 ('forbidden') | application/json | {'message':'Forbidden'} | Invalid token |
| 404 ('not found') | application/json | {'message':'Not Found'} or {'message':'Not Found','errors':['error1', . . . 'errorN'}]} | Can occur because there is an extra or missing path parameter. Can also occur because the path parameters are invalid for creating a product. |
| 500 ('internal server error') | application/json | {'message':'Internal Server Error'} | Encountered an unhandled error. |
Product Formats
Product Filename: S1_<RelativeBurstId>_<Subswath>_<AcquisitionTime>_<Polarization>_<Hashval>-BURST.<FileType>
RelativeBurstId = Burst ID values assigned by ESA, each value identifies a burst cycle, within each sub-swath the burst ID values are unique.
Subswath = Three character combination that represents the acquisition mode and subswath number. The first two characters represent the acquisition mode and the last character identifies the subswath number. (IW)[1..3] or (EW)[1..5]
IW - Interferometric Wideswath. Contains three subswaths over a 250 km swath at 5 m by 20 m spatial resolution.
EW - Extra-Wide Swath. Contains five subswaths over a 400 km swath at 20 m by 40 m spatial resolution.
AcquisitionTime = ISO date of acquisition time.
Polarization = Two character combination that represents the mode of radar orientation for both signal transmission and reception. The first position represents the transmit orientation mode and the second position represents the receive orientation mode.
- HH = Horizontal Transmit - Horizontal Receive
- HV = Horizontal Transmit - Vertical Receive
- VH = Vertical Transmit - Horizontal Receive
- VV = Vertical Transmit - Vertical Receive
Hashval = 4-character "Product Unique Identifier" from the SLC filename.
FileType = Will be either xml for metadata or tiff for GeoTIFF bursts.
XML Products
An XML product is a conglomeration of the entire manifest file and the entirety of every metadata XML file for a given polarization.
TIFF products
A GeoTIFF product is composed of a single burst from a targeted source measurement GeoTIFF file.