Product Details | Hydrosat Docs

Level-1 Imagery

The Level-1A data product is the least processed of the available imagery. It includes processing applied onboard the instrument, such as time delay integration and non-uniformity corrections, as well as co-registration of sensor bands and georegistration. The full swath data is provided to users in image space with no resampling. Level-1A pixel values represent top-of-atmosphere (TOA) radiance [W/m2/sr/μm].

The Level-1B product includes converting the radiance values to TOA reflectance (VIRI) or brightness temperature (LIRI), clipping the VIRI data to the extent of the LIRI swath, generation of a cloud mask, and orthorectification.

L1 Product Granule Size
L1A VIRI: 122 km x 70 km
L1A LIRI: 70 km x 70 km
L1B: Combined 70 km x 70 km

L1 Pixel Size
L1A VIRI: 29.9 m
L1A LIRI: 68.8 m
L1B: 30 m

Resampling Method
Bilinear (L1B only)

Bit Depth
16-bit

Map Projection
L1A VIRI & LIRI: EPSG 4326 (RPCs included in metadata)
L1B: Universal Transverse Mercator (UTM)

No Data Value
0

Scaling Factor
L1A VIRI: 0.01
L1A LIRI: 0.001
L1B VIRI: 0.0001
L1B LIRI: 0.01

Conversion Factors
Coefficients for conversion between radiance and TOA reflectance or BT provided in companion metadata file

Level-1 Assets

Each STAC item includes several assets representing the individual data and metadata files associated with the scene. Items from different collections contain a different set of assets, as defined below.

vz-viri-l1a

vz-liri-l1a

vz-l1b

Conversions

Level-1A VIRI

L1A VIRI TOA radiance values can be converted to TOA reflectance by applying the per-band LEVEL1_REFLECTANCE_SCALING coefficient in the companion L1A metadata (MTA) file.

Level-1A LIRI

L1A LIRI TOA radiance values can be converted to brightness temperature using the following equation:

BT = K2 / ln(K1 / L + 1)

where K1 and K2 are per-band LEVEL1_THERMAL_CONSTANTS from the L1A MTA file, and L represents scaled radiance.

Level-1B VIRI

L1B VIRI reflectance data can be converted back to TOA radiance by applying the per-band LEVEL1_RADIANCE_SCALING coefficient in the companion L1B MTA file.

Level-1B LIRI

L1B LIRI BT values can be converted back to TOA radiance using the following equation:

L = K1 / (e(K2 / BT) - 1)

where K1 and K2 are per-band LEVEL1_BT_TO_RADIANCE_CONSTANTS from the L1B MTA file.

Level-2 Imagery

The Level-2 product includes radiometric terrain corrections and conversion to surface reflectance (SR) and land surface temperature (LST).

L2 Product Granule Size
70 km x 70 km

L2 Pixel Size
30 m

Map Projection
UTM

Bit Depth
16-bit

No Data Value
0

Scaling Factor
LST, LST uncertainty: 0.01
SR, emissivity: 0.0001

Level-2 Assets

Level-2 assets include per-band SR and LST COGs (and more).

vz-l2