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BAS service specifications


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Service Description

The Burned Area Severity Analysis (BAS) service takes calibrated optical data as inputs and estimates the severity of burnt areas by using swir22 and nir radiation from a pair of calibrated optical images.

The burn severity describes how the fire intensity affects the functioning of the ecosystem in the area that has been burnt. The observed effects often vary within the area and between different ecosystems (Keeley, 2009). The burn severity can also be described as the degree to which an area has been altered or disrupted by the fire [RW-01].

The Burned Area Severity Analysis methodology integrated into this service is based on the Normalized Burn Ratio (NBR) index (Key and Benson, 2006) and its derivatives: the delta Normalized Burn Ratio (dNBR) from Miller and Thode (2014), and the Relativized Burn Ratio (RBR) from Parks et al. (2014). Such indexes are described below.

Normalized Burn Ratio and delta Normalized Burn Ratio

The Normalized Burn Ratio (NBR) index developed by Key and Benson, 2006 is defined as the normalized difference between the nir and swir22:

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

The delta Normalized Burn Ratio (dNBR) from Miller and Thode (2014) is defined as:

\[ dNBR = NBR_{prefire} - NBR_{postfire} \]

Relativized Burn Ratio

The Relativized Burn Ratio (RBR) from Parks et al. (2014) is defined as:

\[ RBR = { dNBR \over { NBR_{prefire} + 1.001 } } \]

Also, the processor generates from the pair of input optical images a couple of Shortwave infrared (swir22, nir, red) RGB composites, for both pre- and post-event images.

Workflow

The first step of this processing service creates a collocated stack between the pre and post-event acquisitions of the assets red, nir and swir22.

This collocated stack covers the common area between the pre and the post-event acquisitions.

In case of inputs with different spatial resolution, the higher resolution is used.

The second step applies the band expressions listed below:

\[ NBR_{pre} = { { nir_{pre} - swir_{ {22 pre} } } \over { nir_{pre} + swir_{22 pre} } } \]
\[ NBR_{post} = { { nir_{post} - swir_{ {22 post} } } \over { nir_{post} + swir_{22 post} } } \]
\[ dNBR = NBR_{pre} - NBR_{post} \]
\[ RBR = { dNBR \over { NBR_{prefire} + 1.001 } } \]

The third step generates an RGB composite with:

\[ Red\ channel = swir_{22 post} \]
\[ Green\ channel = nir_{post} \]
\[ Blue\ channel = red_{post} \]

Note

In this service water and cloud masking are not performed. Output products can be masked later (e.g. in QGIS using external available water masks).

Inputs

This processor uses as input calibrated and geocoded L1 or L2 products from the Optical Products Calibration service. The inputs are a pair of optical calibrated products with the assets:

  • red
  • nir
  • swir22

Examples of such missions are:

  • Sentinel-2
  • Landsat-8
  • Worldview-3 (only if swir bands are given)

The pair is typically selected as the pre and post-event acquisition.

Parameters

The BAS 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
Post-event optical calibrated dataset Optical calibrated dataset with red, nir and swir22 assets YES
Pre-event optical calibrated dataset Optical calibrated dataset with red, nir and swir22 assets YES
Area of Interest Area of interest expressed in WKT NO

Table 1 - Service parameters for the BAS processor.

Output

This processing service generates the outputs described below:

Long Name Normalized Burn Ratio pre-event
Short Name nbr_pre
Description Normalized difference between nir and swir22 assets of the pre-event acquisition
Processing level L1 / L2
Data Type Float32
Band Single
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [-1 , 1]
Fill Value N/A

Long Name Normalized Burn Ratio post-event
Short Name nbr_post
Description Normalized difference between nir and swir22 assets of the post-event acquisition
Processing level L1 / L2
Data Type Float32
Band Single
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [-1 , 1]
Fill Value N/A

Long Name Delta Normalized Burn Ratio
Short Name dnbr
Description Difference between the pre and post Normalized Burn Ratio
Processing level L1 / L2
Data Type Float32
Band Single
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [-2 , 2]
Fill Value N/A

Long Name Relativized Burn Ratio
Short Name rbr
Description Relativized Burn Ratio using the pre and post Normalized Burn Ratio
Processing level L1 / L2
Data Type Float32
Band Single
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [-2 , 2]
Fill Value N/A

Long Name Burned Area Severity overview
Short Name overview-bas
Description RGBA composite from a reclassification of RBR index using predefined color operations (from yellow to red shades), including transparency.
Processing level L1 / L2
Data Type Unsigned 8-bit Integer (UInt 8)
Band 4
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [1 - 255]
Fill Value 0

Long Name Shortwave Infrared RGB composite
Short Name overview-sir-pre, overview-sir-post
Description RGBA composite (Shortwave Infrared), including transparency, for both pre- and post-event images.
Processing level L1 / L2
Data Type Unsigned 8-bit Integer (UInt 8)
Band 4
Format COG
Projection EPSG:4326 - WGS84
Units N/A
Valid Range [1 - 255]
Fill Value 0

References

[RE-01] Keeley, J. E. (2009). Fire intensity, fire severity and burn severity: A brief review and suggested usage. International Journal of Wildland Fire, 18(1), 116–126.

[RE-02] 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

[RE-03] Miller J. and Thode A. (2007), “Quantifying burn severity in a heterogeneous landscape with a relative version of the delta Normalized Burn Ratio (RdNBR)”, Remote Sensing of Environment, 109, 66-80. DOI: 10.1016/j.rse.2006.12.006.

[RE-04] Parks S. A., Dillon G. K., Miller C. A. (2014) "A New Metric for Quantifying Burn Severity: The Relativized Burn Ratio" Remote Sens. 6, no. 3: 1827-1844. DOI: 10.3390/rs6031827

[RW-01] UN Spider Knowledge Portal - Normalized burn severity