CEOS Analysis Ready Data (CEOS-ARD) are satellite data that have been processed to a minimum set of requirements and organized into a form that allows immediate analysis with a minimum of additional user effort and interoperability both through time and with other datasets.
Product Family Specification: Optical, Nighttime Light Surface Radiance (NLSR)
Applies to: Data collected with nighttime light sensors operating in the VIS/NIR wavelengths. These typically operate with ground sample distance and resolution in the order of 10-1000m; however, the Specification is not inherently limited to this resolution.
Not available yet
CEOS-ARD products have been processed to a minimum set of requirements and organized into a form that allows immediate analysis with a minimum of additional user effort. These products would be resampled onto a common geometric grid (for a given product) and would provide baseline data for further interoperability both through time and with other datasets.
CEOS-ARD are intended to be flexible and accessible products suitable for a wide range of users for a wide variety of applications, particularly time series analysis and multi-sensor application development. They are also intended to support rapid ingestion and exploitation via high-performance computing, cloud computing and other future data architectures. They may not be suitable for all purposes and are not intended as a replacement for other types of satellite products.
The CEOS-ARD branding is applied to a particular product once:
Agencies or other entities considering undertaking an assessment process should consult the CEOS-ARD Governance Framework or contact ard-contact@lists.ceos.org.
A product can continue to use CEOS-ARD branding as long as its generation and distribution remain consistent with the peer-reviewed assessment.
Threshold (or: minimum) requirements are the minimum that is needed for the data to be analysis ready. This must be practical and accepted by the data producers.
Goal (or: desired) requirements (previously referred to as “Target”) are the ideal; where we would like to be. Some providers may already meet these.
Products that meet all threshold requirements should be immediately useful for scientific analysis or decision-making.
Products that meet goal requirements will reduce the overall product uncertainties and enhance broad-scale applications. For example, the products may enhance interoperability or provide increased accuracy through additional corrections that are not reasonable at the threshold level.
Goal requirements anticipate continuous improvement of methods and evolution of community expectations, which are both normal and inevitable in a developing field. Over time, goal specifications may (and subject to due process) become accepted as threshold requirements.
These are metadata records describing a distributed collection of pixels. The collection of pixels referred to must be contiguous in space and time. General metadata should allow the user to assess the overall suitability of the dataset, and must meet the requirements listed below.
general-metadata-traceability)Data must be traceable to SI reference standard.
Notes:
general-metadata-machine-readability)As threshold, but metadata should be provided in a community endorsed standard that facilitates machine-readability, such as ISO 19115-2.
Metadata is provided in a structure that enables a computer algorithm to be used consistently and to automatically identify and extract each component part for further use.
These are metadata records describing (detailing) each acquisition (source data) used to generate the ARD product. This may be one or mutliple acquisitions, depending on the ARD product.
source-metadata-time)Acquisition time for each pixel is identified (or can be reliably determined) in the metadata, expressed in date/time at UTC, to the second.
The data collection time is identified in the metadata, expressed in date/time, to the second, with the time offset from UTC unambiguously identified.
Information related to the CEOS-ARD product generation procedure and geographic parameters.
product-metadata-geometric-correction-algorithm)Metadata references, e.g.: - A metadata citable peer-reviewed algorithm, - Technical documentation regarding the implementation of that algorithm expressed as URLs or DOIs - The sources of auxiliary data used to make corrections such as elevation model(s) and reference chip-sets. - Resampling method used for geometric processing of the source data.
Notes:
The following minimum 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 applications.
per-pixel-example)This is an example requirement.
This is a goal requirement.
Notes:
This is a threshold requirement.
The following requirements must be met for all pixels in a collection. The requirements indicate both the necessary outcomes and the minimum steps necessary to be deemed to have achieved those outcomes. Radiometric corrections must lead to a valid measurement of surface reflectance.
corrections-measurements-uncertainty)Note: In current practice, users determine fitness for purpose based on knowledge of the lineage of the data, rather than on a specific estimate of measurement uncertainty.
An estimate of the certainty of the values is provided in measurement units.
Notes:
The geometric corrections are steps that are taken to place the measurement accurately on the surface of the Earth (that is, to geolocate the measurement) allowing measurements taken through time to be compared. This section specifies any geometric correction requirements that must be met in order for the data to be analysis ready.
geometric-corrections-corrections-geometric-corrections)Sub-pixel accuracy is achieved relative to an identified absolute independent terrestrial referencing system (such as a national map grid).
A consistent gridding/sampling frame is necessary to meet this requirement.
Relevant metadata must be provided under 1.8 and 1.9.
Notes:
Sub-pixel accuracy is achieved in relative geolocation, that is, the pixels from the same instrument and platform are consistently located, and thus, comparable through time.
Sub-pixel accuracy is taken to be less than or equal to 0.5-pixel radial root mean square error (rRMSE) or equivalent in Circular Error Probability (CEP) relative to a defined reference image.
A consistent gridding/sampling frame is used, including common cell size, origin, and nominal sample point location within the cell (centre, ll, ur).
Relevant metadata must be provided under item 1.8 and 1.9.
Notes: