Day: August 6, 2016
Climate change is arguably the greatest environmental challenge facing us in the twenty-first century. The consequences of a warming climate are far-reaching, potentially affecting freshwater resources, global food production and sea level. Threatening impacts on the natural environment and life on Earth for generations to come, climate change is high on political, strategic and economic agendas worldwide.
The Need for a Global Observing System
Systematic international coordination of weather and climate observations began around the middle of the 19th century and advanced rapidly in the 1960s and 1970s as the advent of digital computers and EO satellites inspired the establishment of the operational World Weather Watch and the Global Atmospheric Research Programme. The great step forward came in the 1980s with the realisation that understanding and predicting climate would require the involvement of a much wider set of scientific communities and comprehensive observation of the entire atmosphere-ocean-land climate system.
Improved understanding of the Earth system – its weather, climate, oceans, land, geology, natural resources, ecosystems and natural and human-induced hazards – is essential if the international climate community is to better predict, adapt and mitigate the expected global changes and their impacts on human civilisation.
Scientists concerned with climate variability and change have, from the very beginning, recognised the importance of observations to the understanding of the atmosphere and the application of atmospheric science to human affairs. Without accurate, high-quality observations on all time and space scales, climate science and services could make only limited progress.
Global Climate Observing System
The Global Climate Observing System (GCOS), was formally established in 1992 by the World Meteorological Organization (WMO), Intergovernmental Oceanographic Commission (IOC), United Nations Environment Programme (UNEP), and International Council for Science (ICSU), as an international, interagency interdisciplinary framework for meeting the full range of national and international needs for climate observations. To meet the need for a systematic observation of climate, the GCOS programme developed the concept of the Essential Climate Variable (ECV). An ECV is a physical, chemical or biological variable or a group of linked variables that critically contributes to the characterization of Earth’s climate.
The Response from Space Agencies
GCOS is progressing the systematic definition of climate information needs in support of the UNFCCC, while Committee on Earth Observation Satellites (CEOS) and Coordination Group for Meteorological Satellites (CGMS), in the form of the Joint CEOS/CGMS Working Group on Climate (WGClimate), is coordinating the planning of the satellite contribution to fulfilling them. To respond to this UNFCCC and GCOS need for climate data, the European Space Agency (ESA) has undertaken the Climate Change Initiative programme. The objective of the Climate Change Initiative is to realise the full potential of the long-term global Earth Observation archives that ESA together with its Member states have established over the last thirty years, as a significant and timely contribution to the ECV databases required by UNFCCC. It ensures that full capital is derived from ongoing and planned ESA missions, including ERS, Envisat, the Earth Explorer missions, relevant ESA-managed archives of Third-Party Mission data and the Sentinel constellation.
The full suite of CCI data products can be accessed via the dedicated CCI ECV project sites : Aerosol,Cloud, Fire, Greenhouse Gases, Glaciers, Ice Sheets, Land Cover, Ocean Colour, Ozone, Sea Ice, Sea Level, Sea Surface Temperature, and Soil Moisture. All CCI data is free to download from these sites and registration procedures, where applicable, are kept to a minimum.
During the summer of 2016, the USGS has made changes to manage the Landsat archive as a tiered Collection of Landsat data. A Collection will provide a stable environmental record. If significant radiometric or geometric changes are required, all data will be reprocessed and a new Collection will be released. The tiered structure clearly identifies the subset of the Landsat archive that meets radiometric and geometric criteria suitable for time series analysis and the creation of data stacks/cubes, while continuing to provide access to the entire Landsat archive.
Starting with Collection 1, every Landsat 4-5 (L4-5) Thematic Mapper (TM), Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 (L8) Operational Land Imager (OLI)/Thermal Infrared Sensor (TIRS) scene is assigned to a specific tier. There are many changes being implemented to Landsat Level-1 data products to support this effort, including new Landsat Product Identifiers, “Collection” and “Tier” designations, metadata changes, and additional supporting files included with Level-1 data products. Higher level products will inherit characteristics of the Level-1 data products.
Collection 1 Tiers
Landsat Tiers are the inventory structure for Landsat Collection 1 Level-1 data products and are based on data quality and level of processing. The purpose of the tier definition is to (1) support rapid and easy identification of suitable scenes for time-series pixel level analysis and (2) provide a holding zone for real-time data prior to the availability of definitive calibration information.
Landsat scenes with the highest available data quality are placed into Tier 1 and are considered suitable for time-series processing analysis. Tier 1 includes Level-1 Precision Terrain (L1TP) processed data that have well-characterized radiometry and are inter-calibrated across the different Landsat sensors. The geo-registration of Tier 1 scenes will be consistent and within prescribed tolerances [≤12m radial root mean square error (RMSE)].
Landsat scenes not meeting Tier 1 criteria during processing are assigned to Tier 2. This includes Systematic Terrain (L1GT) and Systematic (L1GS) processed scenes, as well any L1TP scenes that do not meet the Tier 1 specifications due to significant cloud cover, insufficient ground control, and other factors. Users interested in Tier 2 scenes can analyze the RMSE and other properties to determine the suitability for use in individual applications and studies.
New Landsat Product Identifiers
The Scene ID will remain in the metadata file (MTL.txt) delivered with the Level-1 data product. The heritage Scene ID will also be visible and searchable (along with the new Collection 1 Landsat Product ID) in the online metadata on EarthExplorer.
Processing Level Designation Changes