ALOS PALSAR, ALOS-2 PALSAR-2 and JERS-1 SAR Annual Mosaic

Date modified: 28 Apr 2021

Product overview

Background

Synthetic Aperture Radar (SAR) data have been shown to provide different and complementary information to the more common optical remote sensing data. Radar backscatter response is a function of topography, land cover structure, orientation, and moisture characteristics—including vegetation biomass—and the radar signal can penetrate clouds, providing information about the earth’s surface where optical sensors cannot. Digital Earth Africa provides access to Normalized Radar Backscatter data, for which Radiometric Terrain Correction (RTC) has been applied so data acquired with different imaging geometries over the same region can be compared.

The ALOS/PALSAR annual mosaic is a global 25 m resolution dataset that combines data from many images captured by JAXA’s PALSAR and PALSAR-2 sensors on ALOS-1 and ALOS-2 satellites respectively. This product contains radar measurement in L-band and in HH and HV polarizations. It has a spatial resolution of 25 m and is available annually for 2007 to 2010 (ALOS/PALSAR) and 2015 to 2018 (ALOS-2/PALSAR-2).

The JERS annual mosaic is generated from images acquired by the SAR sensor on the Japanese Earth Resources Satellite-1 (JERS-1) satellite. This product contains radar measurement in L-band and HH polarization. It has a spatial resolution of 25 m and is available for 1996.

These mosaic data part of a global dataset provided by the Japan Aerospace Exploration Agency (JAXA) Earth Observation Research Center.

For more information on the product, see https://www.eorc.jaxa.jp/ALOS/en/palsar_fnf/fnf_index.htm

Specifications

DE Africa provides ALOS/ALOS-2 PALSAR/PALSAR-2 Mosaic and JERS-1 Mosaic as two seperate products. Relevant coverage and metadata can be viewed on DE Africa Metadata Exploer:

Table 1: SAR annual mosaic product specifications

Satellite

JERS-1

ALOS

JERS-2

Instrument

SAR

PALSAR

PALSAR-2

Launch date

Feb 11, 1992

Jan 24, 2006

May 24, 2014

Frequency

L-band (1.27 GHz)

L-band

L-band

Polarisation

HH

HH + HV

HH + HV

Number of bands

4

5

5

Cell size - X (degree)

0.00022

0.00022

0.00022

Cell size - Y (degree)

0.00022

0.00022

0.00022

Coordinate reference system

EPSG:4326

EPSG:4326

EPSG:4326

Temporal resolution

Annual

Annual

Annual

Temporal range

1996

2007-2010

2015 - 2018

More information about the dataset can be found in the dataset description document

Table 2: ALOS/ALOS-2 annual mosaic measurements

Band ID

Description

Data type

No data\(^\dagger\)

HH

HH backscatter

uint16

0

HV

HV backscatter

uint16

0

date

Observation date (days since launch)

uint16

0

linci

Local incidence angle

uint8

0

mask

Processing mask information

uint8

0

\(^\dagger\) No data or fill value.

Backscatter data is provided as digital number (DN), which can be converted to backscatter in decibel unit using \(10*log10(𝐷𝑁^2)-83.0\).

Table 3: JERS annual mosaic measurements

Band ID

Description

Data type

No data\(^\dagger\)

HH

HH backscatter

uint16

0

date

Observation date (days since launch)

uint16

0

linci

Local incidence angle

uint8

0

mask

Processing mask information

uint8

0

\(^\dagger\) No data or fill value.

Backscatter data is provided as digital number (DN), which can be converted to backscatter in decibel unit using \(10*log10(𝐷𝑁^2)-84.66\).

For the ALOS and JERS mosaics, a data mask is provided that can be used to exclude pixels with potentially problematic measurements.

Table 4: Processing mask specification.

Value

Description

0

no_data

50

water

100

lay_over

150

shadowing

255

land

Processing

The ALOS/PALSAR annual mosaic is a global 25 m resolution dataset that combines data from many images captured by JAXA’s PALSAR and PALSAR-2 sensors on ALOS-1 and ALOS-2 satellites respectively. The JERS annual mosaic is generated from images acquired by the SAR sensor on the Japanese Earth Resources Satellite-1 (JERS-1) satellite.

Media and example images

ALOS annual mosaics for crop near Cairo

Figure 1: ALOS false color composites (HH, HV, HV/HH) over an area near Cairo, Egypt, showing changes in crop pattern from year to year.

References

JAXA Global PALSAR-2/PALSAR/JERS-1 Mosaic

License

This dataset is available to use with no charge under the Terms for Use.

Acknowledgements

This dataset is part of a global product provided by the Japan Aerospace Exploration Agency (JAXA).

Data access

Amazon Web Services S3

This product is available in AWS S3.

Table 5: AWS data access details.

AWS S3 details

Bucket ARD

arn:aws:s3:::deafrica-input-datasets

Region

af-south-1

The bucket is in the AWS region af-south-1 (Cape Town). Additional region specifications can be applied as follows:

aws s3 ls --region=af-south-1 s3://deafrica-input-datasets/

The file paths follow the format <productname>/<year>/<tile_id>/.

Table 6: AWS file path convention.

File path element

Description

Example

productname

Product name, alos_palsar_mosaic or jers_sar_mosaic

alos_palsar_mosaic

year

Observation year

2015

tile_id

5x5 deg tile labeld by southwest corner coordinates

S20E020

OGC Web Services (OWS)

This product is available through DE Africa’s OWS.

Table 7: OWS data access details.

OWS details

Name

DE Africa Services

Web Map Services (WMS) URL

https://ows.digitalearth.africa/wms?version=1.3.0

Web Coverage Service (WCS) URL

https://ows.digitalearth.africa/wcs?version=2.1.0

Layer name

alos_palsar_mosaic, jers_sar_mosaic

Digital Earth Africa OWS details can be found at https://ows.digitalearth.africa/.

For instructions on how to connect to OWS, see this tutorial.

Open Data Cube (ODC)

The Landsat Collection 2 Level-2 products can be accessed through the Digital Earth Africa ODC API, which is available through the Digital Earth Africa Sandbox.

ODC product names: alos_palsar_mosaic, jers_sar_mosaic

Specific bands of data can be called by using either the default names or any of a band’s alternative names, as listed in the table below. ODC Datacube.load commands without specified bands will load all bands.

Table 8: ALOS/ALOS-2 annual mosaic (ODC product alos_palsar_mosaic) band names.

Band name

Alternative names

Fill value

hh

0

hv

0

date

0

linci

local incidence angle, incidence

0

mask

0

Table 9: JERS-1 annual mosaic (ODC product jers_sar_mosaic) band names.

Band name

Alternative names

Fill value

hh

0

date

0

linci

local incidence angle, incidence

0

mask

0

Band names are case-sensitive.

For examples on how to use the ODC API, see the DE Africa example notebook repository.

Technical information

Radiometric terrain correction

See relevant section in the Sentinel-1 SAR backscatter product specification.