JAXA Global SAR Mosaics - Preliminary Results & CARD4L Normalised Radar Backscatter

1. Product self-assessment Preliminary results JAXA 25m Global Mosaics to CARD4L Normalised Radar Backscatter Takeo Tadono, Ake Rosenqvist JAXA EORC LSI-VC-7, Hanoi, Vietnam, February 14-15, 2019

2. Global SAR mosaics – Image and Meta data Global SAR mosaic datasets image/data layers: • Radar backscatter (γo) – HH polarisation • Radar backscatter (γo) – HV polarisation • Local incidence angle • Observation date image • Mask image (layover, shadowing, no-data, water) • Data header

3. CARD4L Normalised Radar Backscatter 1 – Radiometric corrections Radiometric corrections - CARD4L spec: The requirements for radiometric corrections must be met for all pixels in a collection. The requirements indicate the necessary outcomes and to some degree the minimum steps necessary to be deemed to have achieved those outcomes. Radiometric corrections must lead to normalised measurement(s) of backscatter intensity. Four parameters: 1. Measurements (γo as Threshold and Target) 2. Noise removal (optional) 3. Terrain Corrections (RTC as Threshold and Target) 4. Radiometric accuracy (uncertainty quantified as Threshold and Target)

4. CARD4L Normalised Radar Backscatter 1 – Radiometric corrections 1°x 1°image tiles LHH LHV JAXA product compliance: Full Radiometric Terrain Correction (RTC) has been undertaken to eliminate incidence angle and topographic effects on the backscatter measurements to render γo, using a peer-reviewed algorithm. The backscatter values are given as (2 byte UINT) linear amplitude. All three sensors (JERS-1 SAR, PALSAR and PALSAR-2) have been subject to absolute calibration (using corner reflectors and radar transponders) and γo can be calculated with the standard formula for amplitude data: γo = 10 * log10(DN2) + K The global SAR mosaics conform with the CARD4L TARGETrequirements for radiometric corrections.

5. CARD4L Normalised Radar Backscatter 2 – Geometric corrections Geometric corrections - CARD4L spec: Geometric corrections must place the measurement accurately on the surface of the Earth (i.e., geolocate the measurement) allowing measurements taken through time to be compared. The geometric accuracy requirements relate to: a) Sub-pixel accuracy b) DEM quality and consistency • Gridding/sampling frame consistency • Relevant metadata relating to geometric accuracy and geometric correction must be provided, • Absolute geolocation is required. Orbit ephemeris updates (precise ephemeris) are required prior to any orthorectification steps to ensure accuracy.

6. CARD4L Normalised Radar Backscatter 2 – Geometric corrections JAXA product compliance: The global SAR mosaics are ortho-rectified using a peer-reviewed algorithm, utilising SRTM Digital Elevation Model. (JERS-1 & ALOS-1: SRTM-90, ALOS-2: SRTM030) In high-latitude regions (>60°N and S), a public open 3-arcsec global DEM is used. The global SAR mosaics meet at least the THRESHOLDrequirements for parameter b (DEM quality and consistency). A study will be being undertaken to assess the compliance with parameters a) and c) (Sub-pixel accuracy; Gridding/sampling frame consistency)

7. CARD4L Normalised Radar Backscatter 3 – General Metadata General Metadata - CARD4L spec: The CARD4L NRB specification for general metadata are records describing a distributed collection of pixels that must be contiguous in space and time. The general metadata should allow the user to assess the overall suitability of the dataset, and must meet Threshold or Target requirements for the following parameters: Traceability Metadata machine readability Data collection time Geographical area Coordinate reference system Map projection Geometric correction Geometric accuracy Instrument Acquisition parameters Processing parameters Sensor calibration Radiometric accuracy Algorithms Ancillary data Processing chain provenance Data access Overall data quality Performance Indicators

8. CARD4L Normalised Radar Backscatter 3 – General Metadata • JAXA product compliance: • Two sources of general metadata are provided for the global SAR mosaics: • an ENVI-formatted header file associated with each of the five image layers, and • a Dataset Description document that is available for download from the JAXA www [8]. • An initial assessment of the general metadata indicate that the SAR mosaics meet the THRESHOLD requirements in six instances (1, 2, 9, 16, 17, 18, 19), TARGET in nine instances (4, 5, 6, 7, 10, 11, 12, 13, 15), and unknown, not applicable or non-compliance in three instances (3, 8, 14). Traceability Metadata machine readability Data collection time Geographical area Coordinate reference system Map projection Geometric correction Geometric accuracy Instrument Acquisition parameters Processing parameters Sensor calibration Radiometric accuracy Algorithms Ancillary data Processing chain provenance Data access Overall data quality Performance Indicators

9. CARD4L Normalised Radar Backscatter 4 – Per-pixel Metadata Per-pixel Metadata - CARD4L spec: The per-pixel metadata specifications apply to each pixel. Whether the metadata are provided in a single record relevant to all pixels, or separately for each pixel, is at the discretion of the data provider. Per-pixel metadata should allow users to discriminate between (choose) observations on the basis of their individual suitability for application. 1. Metadata machine readability 2. No data 3. Layover 4. Shadow 5. Local Incidence Angle 6. Global Incidence Angle 7. Digital Elevation Model 8. Noise Equivalent Sigma0 9. Number of Looks

10. CARD4L Normalised Radar Backscatter 4 – Per-pixel Metadata JAXA product compliance: Per-pixel metadata are provided in the form of 8 or 16 bits image data, with pixel-to-pixel correspondence with the backscatter image data. These include local incidence angle, observation date and data masks for layover, shadowing and no-data. The SAR mosaics meet the THRESHOLD requirements in one instance (1), TARGET in four instances (2, 3, 4, 5), and unknown, not applicable or non-compliance in four instances (6, 7, 8, 9). 1. Metadata machine readability 2. No data 3. Layover 4. Shadow 5. Local Incidence Angle 6. Global Incidence Angle 7. Digital Elevation Model 8. Noise Equivalent Sigma0 9. Number of Looks Local incidence angle Observation date Mask (shadow, layover, no-data)

11. CARD4L Normalised Radar Backscatter Summary This preliminary self-assessment of JAXA’s Global SAR Mosaic datasets against the CARD4L Normalised Radar Backscatter specification indicates that the mosaic products meet the • TARGET requirements for radiometric corrections; • THRESHOLD requirements for one geometric correction parameter, with the other two requiring further investigation; • At least THRESHOLD requirements for 21 out of 28 metadata parameters, with the remaining seven unknown, not applicable or non-compliant. A formal and comprehensive self-assessment is planned to be undertaken by JAXA during 2019, with the aim to make the global SAR mosaics the first SAR data product to be fully compliant with the CARD4L Normalised Radar Backscatter specifications before the end of 2019.

12. CARD4L Normalised Radar Backscatter 以上 (That’s all)