An operational service of new Sentinel-3 algorithms for climate monitoring of the Greenland Cryosphere within the CryoClim network

  1. Monitoring Climate Change in the Cryosphere

Dr. Jason E. Box, Professor, GEUS

Dr. Robert Fausto, Senior Researcher, GEUS

Dr. Kenneth Mankoff, Senior Researcher, GEUS

Background

Arctic warming is more rapid than the global average (IPCC 2014), driving a net mass loss for the Greenland ice sheet that is raising global sea level (e.g. Khan et al. 2015). To provide decision-makers with reliable knowledge, monitoring changes to the Greenland ice sheet change is therefore essential given the global and regional environmental, social and economic impacts.

The operational long-term climate monitoring service of the Cryosphere (CryoClim, www.cryoclim.net), has been developed with past support from the ESA PRODEX program. CryoClim is based on a network of data providers hosted by mandated organizations, which maintain and develop product production chains and repositories. The products are delivered through web services supporting both human and automated users as part of the Global Earth Observation System of Systems (GEOSS) and the Global Cryosphere Watch (GCW) as mandated by the Global Climate Observing System (GCOS) (WMO, 2011). The CryoClim initiative now includes: Norwegian Computing Center (NR), Norwegian Meteorological Institute (MET Norway), Norwegian Water Resources and Energy Directorate (NVE), Norwegian Polar Institute (NPI) and the Geological Survey of Denmark and Greenland (GEUS).

work to be executed

The Sentinel-3 Ocean Land Colour Instrument (OLCI) enables mapping of snow and ice broadband albedo after Kokhanovsky et al. (2018) co-authored by the principal investigator.

The proposed work at GEUS is to operationalize new snow and ice broadband albedo algorithms output from an ESA research contract held by GEUS through end of 2018. That contract delivered (May 2018) an Enhanced (version 2.0) Algorithm Theoretical Basis Document (ATBD) of new and validated algorithms. Yet, no operational product exists.

PRODEX support would enable production for the Greenland region from both Copernicus ESA Sentinel-3A and 3B, accompanied by renewed product verification using the network of 20+ automated weather stations (AWSs) located on the ice sheet through the Programme for Monitoring of the Greenland ice sheet (PROMICE) operated by GEUS.

Our albedo product presently utilizes the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite to monitor the Greenland ice sheet in a systematic way in 18 years of daily gap-filled grids (Box et al. 2017). The proposed work bridges the Copernicus ESA Sentinel-3A, 3B and NASA Terra missions with MODIS on the Terra and Aqua satellites (launched in 1999 and 2002, respectively, and still operating beyond design specification) into a multi decade climate data record of an Essential Climate Variable to satisfy the GCOS snow and albedo essential climate variables (ECVs) mandate (WMO, 2011).

PRODEX support would enable us to transition our product services to the Copernicus Sentinel-3A and 3B data from MODIS. In addition to bridging MODIS and Sentinel data, keeping MODIS part of the mix facilitates identifying issues and to work out how to handle them. An already 2-year overlap between OLCI on Sentinel-3A and the MODIS sensor is also very helpful for cross calibration such that Sentinel-3 can be used as an extension of the MODIS time series.

Ongoing Verification

PI Jason Box and Co-I Robert Fausto participate in Sentinel-3 Validation Team (S3VT)[1] since July 2017. Our S3VT activities include comparison of Sentinel-3 derived surface albedo with ground observations from PROMICE (www.promice.dk) stations situated at more than 20 locations on the Greenland ice sheet.

Direct comparison with field observations from AWSs will be repeated using existing software. The PROMICE network of AWSs allow for a comprehensive validation effort on the proposed deliverables for the CryoClim project. For each of the 8 PROMICE locations (see Appendix), a regularly (each 1-2 years) calibrated radiometer of type CNR-1,4 from Kipp and Zonen is used to validate the satellite derived albedo product. Calibration of PROMICE radiometers undertaken by GEUS at no cost to this proposal ensures SI traceability to the National Physical Laboratory (NPL), UK and Physikalisch-Technische Bundesanstalt (PTB) Germany reference standards.

Incorporating Sentinel-3B data is justified as: 1.) it increases coverage, especially over southern Greenland where Sentinel-3A provides one overpass per day with adequately low solar zenith angles and 2.) makes it easier to identify issues between Sentinel 3A and 3B and work out recommendations, through e.g. S3VT activities, to handle them.

Main Tasks

The project is to implement an operational system for satellite-derived products for the Greenland ice sheet using both EU Copernicus Sentinel-3A and 3B and NASA MODIS data for the period 2000 – through 2020 with the potential for production beyond 2020.

Deliverables

  1. daily snow and ice broadband albedo Level-3 grids
    1. Sentinel-3A and 3B Ocean Land Colour Instrument (OLCI) derived 300 m grids of daily surface albedo, achieved by operationalizing a PI Jason Box (GEUS)-led ESA ATBD[2]
    2. 2000-onward MODIS MOD10A1 v6 calibration after Box et al. (2017)[3]

For the above, sub-tasks include:

  1. development of a production chain at GEUS on existing computers and algorithms already output by ESA SEOM contract ending December, 2018.
  2. verification of time series using existing software applied to observations from the Danish network of 20+ PROMICE automated climate stations[4] synergistic with existing Sentinel-3 Validation Team participation
  3. comparison of Sentinel-3A and 3B albedo products with MODIS products to measure climate data record homogeneity
  4. data posting through CryoClim.net

Project Flow

The work of eight person months is distributed over two years and three senior researchers, organized in an annual cycle with iteration of Sentinel-3A then 3B data based on the OLCI sensor delivered to CryoClim database quarter 4 (Q4) each year. In year 2 two products are delivered covering years 2017-2020 for Sentinel-3A. For Sentinel-3B, products span post-commissioning of 3B until 2020.

    2019       2020      
Sentinel Mission Task Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
3A implementation of production chain x x x
  product verification x
  product delivery to CryoClim portal x x
3B implementation of production chain x x x
  product verification x
  product delivery to CryoClim portal x
  documentation of products x x

[1]              S3VT ID 34609 December 2016: “Sentinel-3 validation over Greenland ice”

[2]                http://snow.geus.dk/index.php/technical-documents/

[3]                Box, J.E., D. van As, K. Steffen, 2017. Greenland, Canadian and Icelandic land ice albedo grids (2000-2016), Geological Survey of Denmark and Greenland Bulletin, 38, 53-56.

[4]                http://promice.dk/home.html