Purpose and objectives:AVHRR LAC expert meeting

Bojan R. BojkovHead, Sensor Performance, Products and Algorithms

Directorate for Earth ObservationESA/ESRIN

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Why AVHRR Local Area Coverage (LAC)?

• 16 missions with AVHRR sensors spanning from 1978 to the present

• AVHRR Local Area Coverage (LAC) data collected through the last 35+ years by ESA and many of its partners organisations.

• AVHRR LAC data rescue and data preservation activities ongoing at DLR, ESA LTDP, U. Bern, USGS, NOAA, etc.

• Scientific interest in the AVHRR LAC dataset, although limited to the station’s receiving area orbits, is high due to the record length, the 1.1 to 2.5km resolution and 2400km swath, and the multiple daily passes.

• The AVHRR record will potentially continue for another decade with the launch of MetOp-C in 2017… and is complimentary to other medium-resolution sensors such as (A)ATSRs, MERIS, MODISs, VIIRSs, as well as the upcoming SLSTR and OLCI sensors on Sentinel-3a,b,c,d.

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Some definitions: Processing levels

Data processing levels (NASA EOS, 1986)

• Level-0 (L0): Reconstructed, unprocessed instrument and payload data at full resolution, with any and all communications artifacts (e. g., synchronization frames, communications headers, duplicate data) removed.

• Level-1a (L1a): Reconstructed, unprocessed instrument data at full resolution, time-referenced, and annotated with ancillary information, including radiometric and geometric calibration coefficients and geo-referencing parameters (e. g., platform ephemeris) computed and appended but not applied to the Level 0 data (or if applied, in a manner that level-0 is fully recoverable from level-1a data).

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Some definitions: Processing levels (ii)

• Level-1b (L1b): Leve-l1a data that have been processed to sensor units (e. g., radar backscatter cross section, brightness temperature, etc.); not all instruments have Level-1b data; level-0 data is not recoverable from level-1b data.

• Level-2 (L2): Derived geophysical variables (e. g., ocean wave height, soil moisture, ice concentration) at the same resolution and location as level-1 source data.

• Level-3 (L3): Variables mapped on uniform space-time grid scales, usually with some completeness and consistency (e. g., missing points interpolated, complete regions mosaicked together from multiple orbits, etc.).

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Some definitions: FCRs and TDRs

Note that no formal definitions for FDR(/FCDR) or TDR(/TCDR) can be found, but using climate/meteorological community descriptions we can define:

• Fundamental Data Records (FDR) are sensor data that have been improved and quality-controlled over time, together with ancillary data used to calibrate them.

• Thematic Data Record (TDR) are geophysical variables derived from FDRs, often generated by blending satellite observations, in-situ data, and model output.

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Some definitions: Cal/Val

Calibration and Validation according to CEOS/WGCV:

• Calibration is the process of quantitatively defining a system’s responses to known, controlled signal inputs.

• Validation is the process of assessing, by independent means, the quality of the data products derived from those system outputs.

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

ESA’s LAC perspective…

• ESA is considering a LAC FDR project for 2015-2018 in close coordination with national AVHRR activities.

• This LAC project would be a combined ESA LTDP and ESA EOEP-4 QA4EO activity, and establish a pre-DISC for AVHRR (DISC: Data Innovation and Science Cluster concept for future ESA R&D).

• It is essential to establish here clear requirements for consolidation, inter-calibration and TDRs, taking into account user requirements.

• The allocated budget depends of the outcome of this expert meeting.

• Potential AVHRR pre-DISC contract KO would be in late 2015, with an initial duration of 36 months.

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

(Inter-)calibration,

generation, and

validation of LAC

FDR

Data

consolidation

and

verification

TDR

generation

and

validation

The potential project setup

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015

Requirements needed on:• Access/ownership• Consolidation level• Auxiliary data• Data format (netCDF)• etc.

…Distributed Archives across ESA member states.

The goal is for sensor data to be physically consistent, but sensor dependent due to differences in frequencies, view angles, resolution, observation time, etc.

Feedback from TDR scientists/developers is critical to ensure best possible FDR dataset for a wide variety of applications.

Provision of “master” dataset

Reminder: the meeting seed questions

• What processing level do you recommend for a harmonised AVHRR multi-sensor dataset? Level-1a or Level-1b?

• Which Level-2 products would most benefit AVHRR Level-1 diagnostics?

• What technical barriers do you see for a multi-sensor 1-km AVHRR dataset? The calibration? The geometric accuracy?

• What approaches and algorithms are most appropriate to process the data?

• What is required (essential) for the multi-sensor dataset in issues of documentation and formats?

• What level of effort/technical barriers do you foresee (for the essential/necessary activities) to achieve a harmonised AVHRR multi-sensor dataset?

• What data policy challenges do you foresee to achieve a harmonised AVHRR multi-sensor dataset? What would be a good compromise to achieve the most complete 1-km AVHRR Level-1 dataset?

AVHRR LAC expert meeting, DLR-Oberpfaffenhofen, 20-21 April 2015