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Hyperspectral

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Product description

The Hyperspectral (HSI) product is a 32-band (Visible and Near infrared) product commonly used for agricultural monitoring, mineral exploration, environmental analysis, and vegetation health assessment, that can be generated from Mark IV and Mark V satellites raw imagery. It is an orthorectified product. This imagery product can be browsed in Telluric Catalog service. It's produced in native resolution, hence having a varying GSD depending on Satellite's altitude and off-nadir angle.

Technical characteristics

Parameter

Mark IV
Sepctral bands

Band 1: 483 nm, FWHM: 15.82
Band 2: 489 nm, FWHM: 16.20
Band 3: 497 nm, FWHM: 16.58
Band 4: 504 nm, FWHM: 16.97
Band 5: 511 nm, FWHM: 17.37
Band 6: 518 nm, FWHM: 17.78
Band 7: 526 nm, FWHM: 18.19
Band 8: 533 nm, FWHM: 18.61
Band 9: 541 nm, FWHM: 19.03
Band 10: 549 nm, FWHM: 19.46
Band 11: 557 nm, FWHM: 19.90
Band 12: 565 nm, FWHM: 20.34
Band 13: 573 nm, FWHM: 20.79
Band 14: 581 nm, FWHM: 21.24
Band 15: 589 nm, FWHM: 21.70
Band 16: 598 nm, FWHM: 22.17
Band 17: 607 nm, FWHM: 22.64
Band 18: 615 nm, FWHM: 23.12
Band 19: 690 nm, FWHM: 27.22
Band 20: 700 nm, FWHM: 27.77
Band 21: 710 nm, FWHM: 28.31
Band 22: 720 nm, FWHM: 28.88
Band 23: 730 nm, FWHM: 29.45
Band 24: 741 nm, FWHM: 30.03
Band 25: 752 nm, FWHM: 30.62
Band 26: 762 nm, FWHM: 31.21
Band 27: 773 nm, FWHM: 31.82
Band 28: 785 nm, FWHM: 32.43
Band 29: 796 nm, FWHM: 33.05
Band 30: 807 nm, FWHM: 33.68
Band 31: 819 nm, FWHM: 34.33
Band 32: 831 nm, FWHM: 34.97
GSD

25m *1
Swath

90 - 145 Km *1
Image bit depth

8-bit for VISUAL, 16 bit for TOA

Max Off-Nadir angle

± 28 deg

Algorithms applied

Radiometric correction, Band Aligment, Geolocation, Projection to UTM

Geolocation Accuracy

<= 100m TBC CE90 *2

Band aligment

<= 8px TBC

Image format

GeoTiff, LZW loseless compression

Ancilliary files

Cloud and usable data mask (GeoTiff), preview (PNG) and thumbnail (PNG).

1 Varies with altitude of the satellites and off nadir angle.
2 Varies with terrain and only applicable for terrains with rich features.

Product presentation

HSI has three subproducts, a VISUAL (RGB) and a radiometrically corrected, top-of-atmosphere, HS version (32 bands). On it's VISUAL version, the output is an 8-bit geotiff and has a streched histogram that enhanced the visibility of the capture for exploration purpouses. The TOA version has a radiometrically corrected 16-bit in units of reflectance and included in the metadata there are coeficcients to convert reflectance into radiance.

drawing The HSI product can be consumed in two presentation or packaging options. As a full scene, or as tiles. A scene is a single image as it was captured by one of Satellogic's satellites. Tiles are a more granular version of the same scene, that can be used for more granular exploration and consumption. Scenes are typically used when users requiere the entire capture that has been tasked using the Tasking API and can also be requested on demand from data found on the archive. Currently, HSI scenes are only available for Tasking orders and delivered to pre-configured AWS S3 bucket. It will become available for download from the API directly.

Projection

This imagery product is projected in UTM, to the corresponding projection parameters according to their closest matching UTM Zone. The projection is indicated in the proj:epsg property of each tile or in the metadata files of each scene. If a scene is captured across different zones, the entire scene and corresponding tiles are projected to the zone with more data.

Product components

Each HSI product, in both tiles and scene presentations have multiple elements associated with them as well as the corresponding metadata.

Thumbnail, preview and raster

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The full resolution raster as well as downsampled versions for preview and thumbnails.





Cloud and usable data mask

drawingdrawing The mask is a single band GeoTiff. The values of the raster represent different cloud data as follows:

  • 0: nodata
  • 1: valid_data
  • 255: cloud

Metadata

Metadata is available for the entire scene in STAC and ISO format, and per tile in STAC format. Common metadata can be found across tiles of the same capture. In tiles, the metadata corresponds to the information of that tile. For scenes, some metadata is aggregated.

The following table shows the description of some of the fields included within the per tile STAC metadata with a corresponding example.

Field Description Example
gsd The ground sampling distance of the image, in meters. 25
datetime Capture date and time of the tile. In UTC 2023-10-03T08:49:16.974867Z
platform Satellite name that acquired the imagery newsat7
grid:code Satellogic 2km grid code for this tile. See below 34N_325_4725
proj:epsg The EPSG projection used corresponding to the UTM zone. See below 32634
eo:cloud_cover The percentage of cloud found on the image, from 0 to 100. 0.02
view:off_nadir The off-nadir angle for the capture measured in degrees. 18.338322997294366
view:sun_elevation The elevation angle of the sun at the target, at the moment of the capture, in degrees. 45.88303237225025
outcome_id A unique identifier, aka sceneset_id, of the associated capture with this tile. d5627157-d1aa-472d-9daa-a55086fd32c2--161551
satl:product_name The unique name of the product of which this tile corresponds to HSI
satl:product_version The version of the product. Uses semantic versioning. 1.1.0
satl:ba_[BAND]_min Mininum band alignment for the [BAND] band and the Red band, in pixels. [BAND] can be Green, Blue. 0.0409754618
satl:ba_[BAND]_max Maximum band alignment for the [BAND] band and the Red band, in pixels. [BAND] can be Green, Blue. 2.6813766514
satl:ba_[BAND]_mean Mean band alignment for the [BAND] band and the Red band, in pixels. [BAND] can be Green, Blue. 0.9747883333
satl:ba_[BAND]_std Standard deviation band alignment for the [BAND] band and the Red band, in pixels. [BAND] can be Green, Blue. 0.7271261225
satl:ba_[BAND]_cep90 CEP90 band alignment for the [BAND] band and the Red band, in pixels. [BAND] can be Green, Blue. 1.3454434311
satl:geoaccuracy_red_min Minimum geoaccuracy error for the red band. 2.4594881332
satl:geoaccuracy_red_max Maximum geoaccuracy error for the red band. 91.9680282423
satl:geoaccuracy_red_mean Mean geoaccuracy error for the red band. 29.9615391065
satl:geoaccuracy_red_std Standard deviation geoaccuracy error for the red band. 12.174708175
satl:geoaccuracy_red_cep90 CEP90 geoaccuracy error for the red band. 35.2145708254
satl:uint16_to_reflectance_[BAND] The scale to apply to the DN value of every pixel to obtain reflecantes units between 0 and 1 . [BAND] can be Red, Green, Blue. Only available for TOA versions of the product. It has a fixed value 0.0001
satl:uint16_to_radiance_[BAND] The scale to apply to the DN value of every pixel to obtain radiance units of W/(m² sr nm) . [BAND] can be Red, Green, Blue. Only available for TOA versions of the product. 0.0005934402

Packaging specification

All the components of the product are included and/or mapped into the two different packacing options, as tiles or as scenes following their corresponding support format.

Tiles

drawing The HSI tiles are available on the Archive STAC API. Each STAC item is a 25km by 25km square tile. They are aligned to a fixed discrete grid, aligned to the prime meridian of each UTM zone (coordinate 500000m). Each tile has a designated grid code included in the property grid:code as follows:

SATL-<GRID SIZE>-<UTM ZONE> _ <X> _ <Y>

Where X and Y correspond to the easting and northing coordinates of the bottom left corner of the tile.

For example the grid:code SATL-25KM-34N_325_4725 should be interpreted as: - SATL grid of 25km by 25km - On UTM zone 34N - With the left bottom corner at 325,000m easting and 4725,000m northing.

Each item/tile contains the following assets/components:

STAC Item asset name Component
analytic The full resolution raster corresponding to the tile.
visual The full resolution RGB raster for visualization.
preview A 128x128 pixels PNG preview of the raster.
thumbnail A 64 x 64 pixels PNG thubmnail of the raster.
cloud The Geotiff cloudmask as defined above.
metadata Json containing all the metadata for all the bands.

Scenes

Scenes are delivered as a single folder or zipped folder. The file name follow the following format: <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_<SPLITTER_ID>, for example like 20231003_084916_SN7_L1_HS_173974. It contains both the TOA, aka analytic, the CLOUD_MASK, and the VISUAL versions of the product.

Inside each package, each file has the prefix <DATE>_<TIME>_SN<SATELLITE_NUMBER>_<SUBPRODUCT>. Where <SUBPRODUCT> can be either HS, VISUAL or CLOUD_MASK. The following files and folders can be found in a typical scene: 

.
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS.vrt
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_CLOUD_MASK.vrt
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L3_HS.vrt
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_footprint.kml
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_metadata.geojson
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_large_preview.png
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_preview.png
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_thumbnail.png
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_geoaccuracy.geojson
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_geoaccuracy_subtile.geojson
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_band_alignment.geojson
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_band_alignment_subtile.geojson
├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_toa_factors.geojson
└── rasters
    ├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_CLOUD_MASK_<UTM-ZONE>_<X>_<Y>.tif
    ├── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L3_HS_<UTM-ZONE>_<X>_<Y>.tif
    └── <DATE>_<TIME>_SN<SATELLITE_NUMBER>_L1_HS_<UTM-ZONE>_<X>_<Y>.tif

File Description
.vrt A GDAL Virtual raster that contains all the corresponding TIFs in the rasters folder. In case of very big images, mutliple tifs can be included in the package.
_footprint.kml The overal raster ground footprint in KML
_metadata.geojson A Metadata file in STAC format containing the aggregated information of the product. See the metada section for more information.
_large_preview.png A large resolution preview of the scene
_preview.png A medium resolution preview of the scene
_thumbnail.png The preview component of the product for the entire scene
_geoaccuracy.geojson A Geojson file that contains all the geoaccuracy metris per tile
_geoaccuracy_subtile.geojson A Geojson file that contains all the geoaccuracy metris per subtile (100 subtiles per tile)
_band_alignment.png A Geojson file that contains all the band alignment metris per tile
_band_alignment_subtile.geojson A Geojson file that contains all the band alignment metris per subtile (100 subtiles per tile)
_toa_factors.geojson A Geojson file that contains the coefficients to transform the TOA product into Radiance units
rasters/_.tif The full resolution rasters that comprise the full scene.

drawing The <PREFIX>_toa_factors.geojson file contains the coefficients for converting the DNs into Radiance and Reflectance units respectively as a geojson tiled filed. The image on the right depicts this file overlaid with the raster file for reference. Small variation of the radiance coefficients can be expected across the image.

Note that, while both have preview and thumbnail png images, they have have different image sizes. In particular, the preview and thumbnail have larger sizes in the scene packaging. Moreover, the scene one contains a large preview png image.

Known issues for current version v1.0.0

  • Thumbnails and previews might present saturated pixels. The analytic raster, HS, does not present the issue.

Changelog

[v0.1.0] 2024-02-08

  • Updated bands and info within the metadata
  • Use internal new quality metrics library
  • Improved radial distortion stage
  • Improved band alignment and geoaccuracy
  • STAC availability

[v0.0.1] 2023-06-31

  • Initial release
Last update: 2024-08-12