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OPT-Index service specifications


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Service Description

The Optical Spectral Index (OPT-Index) service derives multiple spectral indexes from optical remote sensing multispectral data. Spectral indices are derived from a combination of multiple optical bands from calibrated products. This application is able to generate spectral indices given any optical satellite imagery, based on the available spectral bands, independently from its own sensor-specific spectral band naming convention.

Seven radiometric indices (NDVI, NDMIR, NBR, NDWI, NDWI2, MNDWI, NDBI) are available in the ESA Charter Mapper for vegetation, water, fire and built-up classes. Such spectral indices and related formulas are listed below. Formulations are referred to as linear combinations of CBNs.

NDVI - Normalised Difference Vegetation Index

\[ NDVI = { (nir - red) \over (nir + red) } \]

Reference: Rouse et al. (1973)1.

NDMIR - Normalized Difference Middle InfraRed index

\[ NDMIR = { (swir_{16} -swir_{22}) \over (swir_{16} + swir_{22}) } \]

Reference: Lu et al. (2004)2.

NBR - Normalised Burn Ratio

\[ NBR = { (nir - swir_{22}) \over (nir + swir_{22}) } \]

Reference: Key and Benson (2006)3.

NDWI - Normalised Difference Water Index

\[ NDWI = { {(green - nir)} \over {(green + nir)} } \]

Reference: Mc Feeters (1996)4.

NDWI2 - Normalized Difference Water Index 2

\[ NDWI2 = { (nir - swir_{16}) \over (nir + swir_{16}) } \]

Reference: Gao (1996)5.

MNDWI - Modified Normalized Difference Water Index

\[ MNDWI = { (green - swir_{16}) \over (green + swir_{16}) } \]

Reference: Xu (2006)6.

NDBI - Normalised Difference Build-up Index

\[ NDBI = { (swir_{16} - nir) \over (swir_{16} + nir) } \]

Reference: Zha et al. (2003)7.

Workflow

Based on the input optical calibrated product available bands, one or more spectral index are generated.

The workflow is:

graph TB c(cos2) --> d[Dataset] d[Dataset] --> B((Optical<br>calibration)) B((Optical<br>calibration)) --> A[input] subgraph Inputs A aoi[AOI] end subgraph Spectral Index A[input]-->c1{has<br>nir & red?} A[input]-->c2{has<br>green & nir?} A[input]-->c3{has<br>nir & swir22?} A[input]-->c4{has<br>swir16 & swir22?} A[input]-->c5{has<br>nir & swir16?} c1--yes--> D((NDVI)) c2--yes--> E((NDWI)) c3--yes--> F((NBR)) c4--yes--> G((NDMIR)) c5--yes--> H((NDWI2)) c5--yes--> I((NDBI)) D -.-> e{is AOI set?} E -.-> e{is AOI set?} F -.-> e{is AOI set?} G -.-> e{is AOI set?} H -.-> e{is AOI set?} I -.-> e{is AOI set?} e --yes-.-> sp((spatial<br>subset)) aoi -.-> sp end subgraph Output sp -.-> os1[NDVI subset] sp -.-> os2[NDWI subset] sp -.-> os3[NBR subset] sp -.-> os4[NDMIR subset] sp -.-> os5[NDWI2 subset] sp -.-> os6[NDBI subset] e --no-.-> o1[NDVI] e --no-.-> o2[NDWI] e --no-.-> o3[NBR] e --no-.-> o4[NDMIR] e --no-.-> o5[NDWI2] e --no-.-> o6[NDBI] end

Inputs

This service supports Optical EO data from different sensors.

Warning

Input optical EO data must be a calibrated optical multi-spectral dataset. SAR-based indexes are not supported.

Parameters

The OPT-Index service requires a specified number of mandatory and optional parameters. All service parameters are listed in the below Table 1.

Parameter Description Required Default value
Input-reference This parameter is a reference to optical calibrated EO data YES
Area of Interest Area of interest expressed in WKT NO

Table 1 - Service parameters for the OPT-Index processor.

Input product reference

The first parameter represents the reference to the input optical calibrated dataset that is used to generate multiple spectral indexes.

Warning

The input product reference refers to a calibrated optical multi-spectral dataset having at least green, red, and nir assets. Therefore, an Optical Calibrated Dataset having only pan asset cannot be used as input for OPT-Index.

AOI (optional)

This second parameter (optional) may define the area of interest expressed as a Well-Known Text value.

Tip

In the definition of “Area of interest as Well Known Text” it is possible to apply as AOI the drawn polygon defined with the area filter. To do so, click on the Magic tool wizard button in the left side of the "Area of interest expressed as Well-known text" box and select the option AOI from the list. The platform will automatically fill the parameter value with the rectangular bounding box taken from current search area in WKT format.

Outputs

The output of this service is a GeoTIFF in the COG format for each Spectral index product. The creation of output Spectral Index Products depends on the spectral resolution of input Optical EO data. As an example, the Normalized Burn Ratio is produced if both the nir and swir22 bands are available in the input product. For the UK-DMC-2 SLIM-6 data only two possible output Spectral Index Products are derivable from this service which are the NDVI and the NDWI indexes.

The output of OPT-Index is a STAC Item with the output Assets defined as shown in the table below:

Attribute Value / description
Index Normalized Difference Vegetation Index
Short Name ndvi
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Normalized Difference Middle InfraRed index
Short Name ndmir
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Normalised Burn Ratio
Short Name nbr
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Normalised Difference Water Index
Short Name ndwi
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Normalised Difference Water Index 2
Short Name ndwi2
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Modified Normalized Difference Water Index
Short Name mndwi
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN
Attribute Value / description
Index Normalised Difference Build-up Index
Short Name ndbi
Valid range [-1, 1]
Data type Float 32
Band 1
Format COG
Projection Native
No data value NaN

  1. Rouse J., Haas R. H., Schell J. A., Deering D. (1973), “Monitoring vegetation systems in the great plains with ERTS”, NASA. Goddard Space Flight Center 3d ERTS-1 Symp., Vol. 1, Sect. A. Available at: ntrs.nasa.gov 

  2. Lu D., Mausel P., Brondízio, E., Moran E. (2004), “Relationships between forest stand parameters and Landsat TM spectral responses in the Brazilian Amazon Basin”, Forest Ecology and Management, 198, 149-167. DOI: 10.1016/j.foreco.2004.03.048

  3. Key, C. H. and Benson, N. C. (2006), “Landscape Assessment (LA): Sampling and Analysis Methods”, USDA Forest Service Gen Tech. Rep RMRS-GTR-164-CD. FIREMON Fire effects monitoring and inventory System. Available at: fs.fed.us

  4. McFeeters S. K. (1996), “The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features”, International Journal of Remote Sensing, 17:7, 1425-1432, DOI: 10.1080/01431169608948714

  5. Gao B. C. (1996), “NDWI--A normalized difference water index for remote sensing of vegetation liquid water from space”, Remote Sensing of the Environment, 58, 3, 257-266, 0034-4257. DOI: 10.1016/S0034-4257(96)00067-3

  6. Xu H. (2006), “Modification of normalised difference water index (NDWI) to enhance open water features in remotely sensed imagery”, International Journal of Remote Sensing, 27:14, 3025-3033, DOI: 10.1080/01431160600589179

  7. Zha Y., Gao J., Ni S. (2003), “Use of normalized difference built-up index in automatically mapping urban areas from TM imagery”, International Journal of Remote Sensing, 24:3, 583-594, DOI: 10.1080/01431160304987