ECHO Metadata constructs

The following three metadata constructs are utilized by the ECHO system:

• Dataset - A grouping of science data that all come from the same source, such as a modeling group or institution. Datasets have information that is common across all the granules they contain and a template for describing additional attributes not already part of the metadata model.
• Granule - The smallest aggregation of data that can be independently managed (described, inventoried, and retrieved). Granules have their own metadata model and support values associated with the additional attributes defined by the owning dataset.

A dataset within ECHO may contain zero or more granules, however granules cannot exist without being associated to a dataset. Browse images may be associated with either datasets or granules. Browse images may exist in ECHO without an associated dataset or browse, but cannot be discovered in this state. Data Partners should pay close attention to ensure browse image associations are managed closely to eliminate orphaned browse.

Required & Recommended Elements

This section categorizes a subset of all dataset elements into the following perspectives:

• Required Fields – The metadata elements that must be present in order to pass the base XML Schema validation.
• Recommended Fields – The metadata elements that we recommend to facilitate searching and data usability by the science community.

The metadata name and description of each metadata field are listed in tabular form, along with the data type and relevant constraints, where applicable. Only the top-level elements of complex metadata elements are listed. Where this occurs, the requisite child element information is inherently required to correctly represent the parent metadata element.
For a full description of the ECHO data model, refer to the schema and documentation referenced on the ECHO Website (http://api.echo.nasa.gov/ingest/).

Datasets

Required Elements

Recommended Elements

Granules

Required Elements

Recommended Elements

Temporal Data

Temporal metadata refer to the date and time associated with the data represented within a dataset or granule. This is also commonly referred to as ―acquisition date and time.‖ Temporal data is an essential search criteria for datasets and granules within ECHO. Temporal information is not a required element for datasets or granules. However, if a granule specifies temporal information, the dataset must also. ECHO Ingest will validate that a granule's temporal data falls within the range of its owning dataset's temporal data. If a dataset specifies an open ended temporal range, ECHO will accept all granules that provide temporal data that is subsequent to the dataset's starting date.

Datasets

A dataset may be associated with one or more of the following three types of temporal expressions:

• Single Date Time – A single date and time.
• RangeDateTime – A date and time range specified by a beginning and ending date and time. An ending date is not required in order to designate an on-going dataset. 
• PeriodicDateTime – A repeating date and time range specified by a beginning and ending date and time with a period cycle and duration.

A dataset may provide more than one instance of a single type of temporal expression. For instance, there may be two ranges associated with the dataset signifying that there was a period of time for which no data was collected. ECHO will facilitate discovery of all temporal information, however it will also calculate an internal beginning and ending date/time based upon the least or greatest (respectively) value provided in the list of temporal expressions.
These expressions are used to provide the necessary information in order to uniquely identify the temporal range for which data may be discovered within the dataset. In addition to these items, you may also specify the following items providings users with additional information regarding the temporal specifications of the dataset:

• TimeType – The time system which time values found in the temporal ranges represent. (e.g. UTC)
• DateType – The type of date represented by the value in the temporal ranges represent. (e.g. Gregorian) 
• TemporalRangeType – Designates how the temporal coverage is specified. (e.g. Continuous Range) 
• PrecisionofSeconds – The precision of seconds used in the measurement 
• EndsAtPresent – Boolean flag denoting that a data dataset which covers, temporally, a discontinuous range, currently ends at the present date. This way, the granules, which comprise the data dataset, that are continuously being added to inventory need not update the data dataset metadata for each one.

<Temporal> 
	<TimeType>UTC</TimeType> 
	<DateType>Gregorian</DateType>
	<TemporalRangeType>Continuous Range</TemporalRangeType> 
	<PrecisionofSeconds>1</PrecisionofSeconds> 
	<EndsatPresentFlag>Y</EndsatPresentFlag> 
	<RangeDateTime>
		<BeginningDateTime>1998-01-01T00:00:00.0Z</BeginningDateTime> 
	</RangeDateTime>
</Temporal> 

Granules

A granule may be associated with one of the following two types of temporal expressions:

• SingleDateTime – A single date and time.
• RangeDateTime – A date and time range specified by a beginning and ending date and time. An ending date is not required in order to designate an on-going granule.

A granule may provide more than one instance of a single type of temporal expression. For instance, there may be two ranges associated with the granule signifying that there was a period of time for which no data was collected. ECHO will facilitate discovery of all temporal information, however it will also calculate an internal beginning and ending date/time based upon the least or greatest (respectively) value provided in the list of temporal expressions.
These expressions are used to provide the necessary information in order to uniquely identify the temporal range for which data in the granule represents.

<Temporal> <RangeDateTime>
<BeginningDateTime>1998-01-01T00:00:00.0Z</BeginningDateTime> <EndingDateTime>1998-01-01T00:00:00.0Z</EndingDateTime>
</RangeDateTime> </Temporal> 

Spatial Data

Cartesian/Geodetic/Orbital Information

For a full description of ECHO spatial representations, please refer to ECHO spatial representations.

Two-Dimensional Coordinate System

In order to facilitate discovery based upon an additional mechanism, a two-dimensional coordinate system may be used. Examples of two-dimensional coordinate system values are path/row for Worldwide Reference System (WRS) data and Moderate Resolution Imaging Spectroradiometer (MODIS) tiles IDs. A dataset must define all two dimensional coordinate systems that granules in that dataset may use. ECHO Ingest will validate that a granule's TwoDCoordinateSystem element references a valid coordinate system defined in the dataset. If the dataset's definition for the coordinate system defines minimum and maximum values for the system axes, ECHO Ingest will validate the granule's metadata against these constraints.

Coordinate System Axis Labels

The ECHO data model does not allow providers to configure axis labels for each TwoDCoordinateSystem. This was chosen to avoid issues where the same coordinate system in two datasets contains different labels for the same axis. This would be a significant issue for ECHO Client Developers. ECHO has chosen to identify the following unique coordinate systems, with the axis labels included below. This listing of labels is recommended for ECHO Client Partners and is used in WIST. If additional coordinate systems are utilized, Data Partners should coordinate with ECHO Operations to ensure that the labeling recommendations are correct.

Datasets

The Two-Dimensional Coordinate System information that exists at the dataset level and contains the following information:

• TwoDCoordinateSystemName – The identifying name of the coordinate system
• Start/EndCoordinate1 – The ‗X' axis coordinate minimum and maximum range values 
• Start/EndCoordinate2 – The ‗Y' axis coordinate minimum and maximum range values

The minimum and maximum range values are not required for both the ‗X' and ‗Y' axes. This allows for finite, infite (in both directions), or no range validation for a specific coordinate system axis. The following example provides a finite range for Coordinate1 and infinite ending for Coordinate 2.

<TwoDCoordinateSystem> 
	<TwoDCoordinateSystemName>WRS2</TwoDCoordinateSystemName> 
		<Coordinate1>
			<MinimumValue>0</MinimumValue> 
			<MaximumValue>38</MaximumValue>
		<Coordinate1/> 
		<Coordinate2>
			<MinimumValue>0</MinimumValue> 
		<Coordinate2/>
</TwoDCoordinateSystem> 

Granules

The Two-Dimensional Coordinate System information that exists at the granule level and contains the following information:

• Start/EndCoordinate1 – The ‗X' axis start and end (not required) coordinate values
• Start/EndCoordinate2 – The ‗Y' axis start and end (not required) coordinate values 
• TwoDCoordinateSystemName – The identifying name of the coordinate system

<TwoDCoordinateSystem> <StartCoordinate1>21</StartCoordinate1> <StartCoordinate2>29</StartCoordinate2> <EndCoordinate2>33</EndCoordinate2> <TwoDCoordinateSystemName>WRS2</TwoDCoordinateSystemName>
</TwoDCoordinateSystem> 

Additional Attributes

Additional attributes are parameters, also known as Provider-Specific Attributes (PSAs), which further describe the data represented in each granule within a dataset. These values are important search criteria for the granules. Example attributes include values for cloud cover, MODIS Tile grid coordinates, and elevation information. All additional attribute definitions are included in the dataset metadata. A dataset may also specify a value, to be understood as the value for all granules. Granules reference defined additional attributes and supply a value that is associated to that granule. Granules may not define a new additional attribute that is not defined by the dataset.
The following table shows the supported additional attribute data types that within ECHO. The ―XML Type‖ table lists the XML schema type that will be used to validate any attribute values specified in the dataset of granules. The Range Validation column specifies whether range values are allowed at the dataset level, and, if present, whether granules additional attribute values will be validated against the supplied ranges. The *_STRING types allow providers to specify date, time, and datetime attribute values without the associated data validation performed for the pure date and time types.

Datasets

An additional attribute, as defined within dataset metadata, must include the following information:

• Name – Unique name of the additional attribute.
• DataType – Data type of the additional attribute, chosen from the supported list of types. 
• Description – A textual description of the attribute to help end users understand the purpose and data represented by the attribute.

Your additional attribute definition may also contain the following elements providing additional information:

• MeasurementResolution – Identifies the smallest unit increment to which the parameter value is measured.
• ParameterRangeBegin – Minimum value of all attribute values that will be provided by the dataset or granules.
• ParameterRangeEnd – Maximum value of all attribute values that will be provided by the dataset or granules.
• ParameterUnitsOfMeasure – Unit of measure for parameter (e.g. AVHRR: unit of geophysical parameter-units of geophysical parameter.) 
• ParameterValueAccuracy – Estimate of the accuracy of the assignment of attribute value. This can be specified in percent or the unit with which the parameter is measured. 
• ValueAccuracyExplanation – Defines the method used for determining the parameter value accuracy.

As was discussed previously, ECHO Ingest will perform value validation based upon the attribute's data type and range values. See the table in the previous section for more information regarding validation.

<AdditionalAttributes>
	<AdditionalAttribute> 
		<Name>PROCESSVERSION</Name> 
		<DataType>STRING</DataType>
		<Description>foo</Description> 		
	</AdditionalAttribute>
	<AdditionalAttribute> 
		<Name>HORIZONTALTILENUMBER</Name> 
		<DataType>INT</DataType> 
		<Description>foo</Description>		
		<ParameterRangeBegin>1</ParameterRangeBegin>
		<ParameterRangeEnd>100</ParameterRangeEnd>
	</AdditionalAttribute> 
</AdditionalAttributes> 

Granules

An additional attribute, as defined within granule metadata, must include the following information:

• Name – Unique name of the additional attribute as defined by the dataset.
• Values – One or more values for the additional attribute.

As was discussed previously, ECHO Ingest will validate that an additional attribute with the same name is defiend within the granule's dataset. Also, Ingest may perform value validation based upon the attribute's data type and range values. See the table in the previous section for more information regarding validation. If more than one value is provided, ECHO will preserve the order of the values when queried through the ECHO API.

<AdditionalAttributes> 
	<AdditionalAttribute>
		<Name>VERTICALTILENUMBER</Name> 
		<Values>
			<Value>12</Value> 
		</Values>
	</AdditionalAttribute> 
	<AdditionalAttribute>
		<Name>TileID</Name> 
		<Values>
			<Value>51013012</Value> 
			<Value>51013013</Value>
		</Values> 
	</AdditionalAttribute>
</AdditionalAttributes> 

Platforms, Instruments And Sensors

ECHO adopts a layered representation of platforms, instruments (also known as sources), and sensors in dataset and granule metadata. This layered representation is as follows:

All possible platforms, instruments, and sensors that may exist within the granules must be defined with the dataset metadata. A dataset could be associated with zero (0) or more platforms; each platform could contain zero (0) or more instruments, and each instrument could contain zero (0) or more sensors. Each item is uniquely identified by that item's ShortName element value. Granules reference defined platform/instrument/sensor combinations associated to that granule. Granules may not define a new platform/instrument/sensor combination that is not defined by the dataset.
The platform, instrument, and sensor must comply with the GCMD standard, located at http://gcmd.gsfc.nasa.gov/Resources/valids/index.html.

Datasets

A platform has the following information that is included in the dataset definition:

• ShortName – Unique name of the platform within the dataset.
• LongName – The expanded or long name of the platform associated with an instrument. (Required) 
• Type – The most relevant platform type. (Required) 
• Characteristics – The characteristics of platform specific attributes. The characteristic names must be unique on this platform; however the names do not have to be unique across platforms.

An instrument has the following information that is included in the dataset definition:

• ShortName – Unique name of the platform within the dataset.
• LongName – The expanded name of the primary sensory instrument. 
• Technique - Technique applied for this instrument in the configuration. 
• NumberOfSensors - Number of sensors used on the instrument when acquire the granule data. 
• Characteristics - The characteristics of this instrument expressed as custom attributes. The characteristic names must be unique on this instrument; however the names do not have to be unique across instruments. 
• OperationModes - The operation mode applied on the instrument when acquire the granule data.

A sensor has the following information that is included in the dataset definition:

• ShortName – Unique name of the sensor within the dataset.
• LongName – The expanded name of the sensor. 
• Technique - Technique applied for this sensor in the configuration. 
• Characteristics - The characteristics of this sensor expressed as custom attributes. The characteristic names must be unique on this instrument; however the names do not have to be unique across sensor.

<Platform> 
	<ShortName>Terra</ShortName> 
	<LongName>First EOS Polar Orbiting Satellite, 10:30 AM Descending Equator Crossing </LongName>
	<Type>Spacecraft</Type> 
	<Characteristics>
		<Characteristic> 
			<Name>EquatorCrossingTime</Name> 
			<Description>Local time of the equator crossing and direction (ascending or descending)</Description> 
			<DataType>varchar</DataType> 
			<Unit>Local Mean Time</Unit> 
			<Value>10:30, descending</Value>
		</Characteristic> 
	</Characteristics> 
	<Instruments>
		<Instrument> 
			<ShortName>MODIS</ShortName> 
			<LongName>Moderate-Resolution Imaging Spectroradiometer</LongName>
			<Technique>Imaging Spectroradiometry</Technique> 
			<NumberOfSensors>2</NumberOfSensors> 
			<Characteristics />
			<Sensors> 
				<Sensor>
					<ShortName>MODIS</ShortName>
					<LongName>Cross-track Scanning Radiometer</LongName> 
					<Technique>Radiometry</Technique>
					<Characteristics /> 
				</Sensor>
			</Sensors> 
		</Instrument>
	</Instruments> 
</Platform> 

Granules

A platform has the following information that is included in the granule metadata:

• ShortName – Unique name of the platform within the dataset.

An instrument has the following information that is included in the granule metadata:

• ShortName – Unique name of the platform within the dataset.
• Characteristics - The characteristics of this instrument expressed as custom attributes. The characteristic names must be unique on this instrument; however the names do not have to be unique across instruments. 
• OperationModes - The operation mode applied on the instrument when acquire the granule data.

A sensor has the following information that is included in the granule metadata:

• ShortName – Unique name of the sensor within the dataset.
• Characteristics - The characteristics of this sensor expressed as custom attributes. The characteristic names must be unique on this instrument; however the names do not have to be unique across sensor.

As was discussed previously, ECHO Ingest will validate that an additional attribute with the same name is defiend within the granule's dataset. Also, Ingest may perform value validation based upon the attribute's data type and range values. See the table in the previous section for more information regarding validation. If more than one value is provided, ECHO will preserve the order of the values when queried through the ECHO API.

<Platform> <ShortName>Terra</ShortName> <Instruments>
<Instrument> <ShortName>MODIS</ShortName> <Sensors>
<Sensor> <ShortName>MODIS</ShortName>
</Sensor> </Sensors>
</Instrument> </Instruments>
</Platform>

Measured Parameters

Measured parameters are associated only at the granule level only and are important search criteria for granules. For some providers, the value of certain measured parameters determines the visibility of the granule.
Measured parameters contain the name of the geophysical parameter expressed in the data as well as associated quality flags and quality status. The quality status contains measures of quality for the granule. The parameters used to set these measures are not preset and will be determined by the data producer. Each set of measures can occur many times either for the granule as a whole or for individual parameters. The quality flags contain the science, operational and automatic quality flags that indicate the overall quality assurance levels of specific parameter values within a granule.
A measured parameter is uniquely identified by its ParameterName element, and has the following information:

• QAStats – The name of the geophysical parameter expressed in the data as well as associated quality flags and quality status
  • QAPercentMissingData - Granule level % missing data. This attribute can be repeated for individual parameters within a granule. 
  • QAPercentOutOfBoundsData – Granule level % out of bounds data. This attribute can be repeated for individual parameters within a granule.
  • QAPercentInterpolatedData – Granule level % interpolated data. This attribute can be repeated for individual parameters within a granule. 
  • QAPercentCloudCover – This attribute is used to characterize the cloud cover amount of a granule. This attribute may be repeated for individual parameters within a granule. (Note - there may be more than one way to define a cloud or it's effects within a product containing several parameters; i.e. this attribute may be parameter specific) 
• QAFlags – The name of the geophysical parameter expressed in the data as well as associated quality flags and quality status. 
  • AutomaticQualityFlag – The granule level flag applying generally to the granule and specifically to parameters the granule level. When applied to parameter, the flag refers to the quality of that parameter for the granule (as applicable). The parameters determining whether the flag is set are defined by the developer and documented in the Quality Flag Explanation. 
  • AutomaticQualityFlagExplanation – A text explanation of the criteria used to set automatic quality flag, including thresholds or other criteria. 
  • OperationalQualityFlag – The granule level flag applying both generally to a granule and specifically to parameters at the granule level. When applied to parameter, the flag refers to the quality of that parameter for the granule (as applicable). The parameters determining whether the flag is set are defined by the developers and documented in the Operational Quality Flag Explanation. 
  • OperationalQualityFlagExplanation – A text explanation of the criteria used to set operational quality flag; including thresholds or other criteria. 
  • ScienceQualityFlag – Granule level flag applying to a granule, and specifically to parameters. When applied to parameter, the flag refers to the quality of that parameter for the granule (as applicable). The parameters determining whether the flag is set are defined by the developers and documented in the Science Quality Flag Explanation. 
  • ScienceQualityFlagExplanation – A text explanation of the criteria used to set science quality flag; including thresholds or other criteria.

<MeasuredParameters> <MeasuredParameter>
<ParameterName>Snow_Cover_Daily_Tile</ParameterName> <QAStats>
<QAPercentMissingData>0</QAPercentMissingData> <QAPercentCloudCover>65</QAPercentCloudCover>
</QAStats> <QAFlags>
<AutomaticQualityFlag>Passed</AutomaticQualityFlag> <AutomaticQualityFlagExplanation>
No automatic quality assessment done in the PGE </AutomaticQualityFlagExplanation> <OperationalQualityFlag>Passed</OperationalQualityFlag> <OperationalQualityFlagExplanation>
Passed </OperationalQualityFlagExplanation>
<ScienceQualityFlag>Not Investigated</ScienceQualityFlag> <ScienceQualityFlagExplanation>
See http://landweb.nascom.nasa.gov/cgi-bin/QA_WWW/qaFlagPage.cgi? sat=terra for the product Science Quality status.
</ScienceQualityFlagExplanation> </QAFlags>
</MeasuredParameter>
</MeasuredParameters> 

Online Data Access URL And Online Resources URL

For some granules or datasets, the raw data are made available online via FTP or web URL. ECHO stores this online access information for directly accessible granule and dataset data differently from information covering other aspects of granule and dataset data. Directly accessible data require the <OnlineAccessURLs> tag and include the URL to that data. Use OnlineAccessURLs only for the actual data. Online access URLs specified in dataset and granule metadata include the following elements:

• URL – URL for the online data. (Required)
• URLDescription – Description of the data available via the supplied URL. 
• MimeType – The mime type of the online data.

Any other online information covering aspects of the data, such as guides, product listings, validation information, etc., should be listed in an <OnlineResources>, along with the URLs to that information. Online resource URLs specified in dataset and granule metadata include the following elements:

• URL – URL for the online resource. (Required)
• URLDescription – Description of the resource available via the supplied URL. 
• Type - The type of the resource such as 'Dataset Guide' or 'Campaign Guide' etc. This value should be a short phrase that can be used in an ECHO client for displaying the URL. (Required) 
• MimeType – The mime type of the online resource

<OnlineAccessURLs> 
	<OnlineAccessURL>
		<URL>ftp://daac.nasa.gov/granule_1234.zip</URL> 
		<URLDescription>Compressed data granule</URLDescription> 
		<MimeType>application/zip</MimeType>
	</OnlineAccessURL> 
</OnlineAccessURLs>
<OnlineResources> 
	<OnlineResource>
		<URL>http://daac.nasa.gov/products/product_A.html</URL> 
		<URLDescription>Main product overview page.</URLDescription> 
		<Type>Product Overview</Type>
		<MimeType>text/html</MimeType> 
	</OnlineResource>
</OnlineResources> 

Keywords

ECHO supports three kinds of keyword associations for datasets: science keywords, spatial keywords, and temporal keywords. Science keyword and spatial keyword values should come from the Global Change Master Directory (GCMD) keywords standard located at http://gcmd.nasa.gov/learn/keyword_list.html.
Currently, the ECHO structure for Science Keywords matches the GCMD standard, however the Spatial Keywords do not. There is no published Temporal Keywords list managed by GCMD.Science Keywords

The science keyword metadata element fully implements the GCMD keyword hierarchy, which contains the following fields. There are no associated granule metadata elements for the science keyword.

• Category –. Keyword used to describe the general category of the dataset.
• Topic – Keyword used to describe the general topic of the dataset. 
• Term – Keyword used to describe the science parameter area. 
• VariableLevel1 – Keyword containing the first level science keyword variable. 
• VariableLevel2 – Keyword containing the second level science keyword variable. 
• VariableLevel3 – Keyword containing the third level science keyword variable. 
• DetailedVariable– Keyword containing a ree form field for further keyword specification.

<ScienceKeywords> 
	<ScienceKeyword>
		<CategoryKeyword>EARTH SCIENCE</CategoryKeyword> 
		<TopicKeyword>ATMOSPHERE</TopicKeyword> 
		<TermKeyword>ATMOSPHERIC CHEMISTRY</TermKeyword> 
		<VariableLevel1Keyword>
			<Value>OXYGEN COMPOUNDS</Value> 
		</VariableLevel1Keyword>
	</ScienceKeyword> 
</ScienceKeywords>

Spatial Keywords

The spatial keyword metadata element does not currently implement the updated GCMD keyword hierarchy. The ECHO spatial keyword contains a single value, which can be understood to be the ‗Location' field in the GCMD managed list of keywords. There are no associated granule metadata elements for the science keyword.

<SpatialKeywords>
	<Keyword>GEOGRAPHIC REGION</Keyword> 
</SpatialKeywords> 

Temporal Keywords

The temporal keyword metadata element does not associated with a GCMD managed keyword list. The ECHO spatial keyword contains a single value. There are no associated granule metadata elements for the science keyword.

<TemporalKeywords> 
	<Keyword>UTC</Keyword>
</TemporalKeywords>