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View Metadata

View Metadata

Use View Metadata to view detailed properties of the following types of data:

  • Raster
  • Vector
  • Raster Color Slices
  • Classification
  • Esri® layers
  • Annotation

Double-click the layer name in the Layer Manager, or right-click and select View Metadata. The Metadata Viewer appears. Here are some tips for working with the Metadata Viewer:

  • Click each node on the left side of the dialog to see values for each of its properties. An example node is "Raster," and an example property for Raster is "Dataset." You cannot edit metadata fields from this dialog.
  • The "Coordinate System" node displays map properties for datasets georeferenced to a geographic or projected coordinate system. An "RPC Map Info" node is available for datasets mapped with rational polynomial coefficients (RPCs) instead of a map projection. This node displays the properties of the coefficients.
  • Click a node on the left side of the Metadata Viewer and click Export to export the properties for that node, or all nodes, to a text file.
  • If you opened a georeferenced dataset into the Image window view, you can see the coordinate system properties of the view. Right-click on a view name in the Layer Manager and select View Properties.
  • Click the Edit Metadata button to edit the metadata fields as needed. See the Edit Raster Metadata topic for further instructions.

Most metadata fields are self-explanatory, however some groups of metadata require further explanation:

Calibration Metadata


See the Radiometric Calibration topic for a list of sensors that ENVI automatically reads spectral calibration metadata from. The Metadata Viewer will then show the following fields (per band) under the "Spectral" category:

  • Wavelengths: Units vary by sensor.
  • FWHM: Full-width-half-maximum. Units vary by sensor; they must be in the same units as the wavelengths for a given file.
  • Gains: Units are W/(m2 * sr * µm).
  • Offsets: Units are Units are W/(m2 * sr * µm).
  • Irradiance: Solar irradiance; units are W/(m2 * µm).
  • Reflectance Gains: No units.
  • Reflectance Offsets: No units.
  • Thermal Infrared 1 and Thermal Infrared 2: The K1 and K2 constants used to compute brightness temperatures. For Landsat TM and ETM+, these values are hard-coded from the publication Chander, Markham, and Helder (2009). For Landsat-8, these values are read from the _MTL.txt metadata files.

The following fields are listed under the "Image Parameters" category:

  • Cloud Cover: Percentage of cloud cover within the image.
  • Sun Azimuth: Angle of the sun (in degrees) from due north in a clockwise direction.
  • Sun Elevation: Angle of the sun (in degrees) above the horizon.

The following fields are listed under the "Supplementary" category:

  • Earth Sun Distance: ENVI computes the earth-to-sun distance (in Astronomical Units), using the following equation from The Astronomical Almanac for the Year 2013:
  • d = 1.00014 - 0.01671*cos(g) - 0.00014*cos(2g)

    Where:

    g = 357.528 + 0.9856003n

    g is then converted to radiance using the following equation: g = g*(pi/180)

    n = Julian Day - 2451545

If you save a dataset from any of these sensors to ENVI raster format, the accompanying header file (.hdr) will contain the following metadata fields: band names, bbl, cloud cover, data gain values, data offset values, fwhm, solar irradiance, sun azimuth, sun elevation, and wavelength.

Note: If you are programming with the ENVI API, all inherent metadata (including calibration parameters) is stored in memory as a property to the raster object. See ENVIRaster and ENVIRasterMetadata for more information.

References:

Chander, G., B. Markham, and D. Helder, "Summary of current radiometric calibration coefficients for Landsat MSS, TM, ETM+, and EO-1 ALI sensors," Remote Sensing of Environment 113 (2009): 893-903.

Irons, J., J. Dwyer, and J. Barsi, "The next Landsat satellite: The Landsat Data Continuity Mission," Remote Sensing of Environment 122 (2012): 11-21.

The Astronomical Almanac for the Year 2013. Joint publication of the U.S. Naval Observatory and Her Majesty's Nautical Almanac Office. St. Louis, MO: US Government Printing Office, 2012.

Acquisition Time


ENVI reads data acquisition time for ENVI-format files if the accompanying header file (.hdr) contains an acquisition time value. The acquisition time is listed under the "Time" category of the Metadata Viewer.

For Landsat, Pleiades, SPOT, QuickBird, and WorldView files, ENVI reads the data acquisition time from the metadata files distributed with the imagery.

  • For DubaiSat, Landsat, Pleiades, and SPOT, the acquisition time is the scene center time.
  • For Pleiades tiled products, the acquisition time is the beginning time of the first tile.
  • For EO-1 ALI, Gaofen-1, Hyperion, Ziyuan-1-02C, and Ziyuan-3A data, the acquisition time is the scene start time.
  • For QuickBird and WorldView, acquisition time is taken from the firstLineTime field for basic products or the earliestAcqTime field for projected products.

If you save an image from any of these sensors to ENVI format, an acquisition time field will be added to the ENVI header file.

Note: If you are programming with the ENVI API, all inherent metadata (including acquisition time) is stored in memory as a property to the raster object. See ENVIRaster and ENVIRasterMetadata for more information. You can also create an ENVITime object that stores the acquisition time for a given raster dataset.

NITF Metadata


You can also view metadata for NITF datasets including header information, tagged record extensions (TREs), data extension segments (DESes), annotation segments, and text segments. The metadata displayed in each item vary per different versions of NITF.

You can also write a script to view NITF metadata using the ENVINITFMetadata function.

See NITF Metadata Icons for a description of each item. Metadata are grouped as follows:

File Header

  • Security Metadata
  • TRE Metadata (if present)

Image Segment

  • Security Metadata
  • Band Metadata (one for each band)
  • Image Comments (if present)
  • TRE Metadata (if present)

Text Segment (if present)

  • Security Metadata
  • TRE Metadata (if present)

Data Extension Segments (DESes, if present)

  • Security Metadata
  • User-defined Subheader (if present)

Annotation Segments (if present)

  • Security Metadata
  • Annotation Object Metadata (if present)
  • TRE Metadata (if present)

Note: Header and segment fields are described in MIL-STD-2500C and MIL-STD-2500A.

NITF Metadata Icons

The following icons appear in the Metadata Viewer to identify the types of metadata that may appear in a particular container:

Container

Icon

Description

File Header

Contains metadata common to the entire NITF file. It may also include tags (TREs) or security metadata pertaining to the entire file.

Security

Contains security metadata for the file, image segment, text segment, annotation segment, or data extension segment.

TRE



A white icon contains metadata for a TRE that cannot be edited.
A green icon contains editable metadata for the TRE.
A blue icon contains TREs from a TRE Overflow DES.

DES

Contains Data Extension Segments (DESes). It may also include security metadata and user-defined subheader fields.

Single-band Image Segment

Contains image metadata for a single-band image segment. It may also include security metadata, image comments, and TRE metadata containers.

Multi-band Image Segment

Contains image metadata for a multiple-band image segment. It may also include security metadata, image comments, and TRE metadata containers.

Annotation Segment

Contains metadata for an annotation segment. In addition to one or more annotation object containers, it may also include security tag metadata containers.

Text Segment

Contains metadata for a text segment.

TIFF Metadata


For TIFF and GeoTIFF image files, you can optionally use the Edit ENVI Header tool or a text editor to create an ENVI header file (.hdr) to override the default metadata fields. For example, you can change the default stretch type to better visualize the data or you can change the wavelength information if you know that it is wrong in the original TIFF/GeoTIFF file. Once you save the changes to a header file, ENVI will read the new metadata values when you re-open the image file.

Raster Series Metadata


These metadata fields pertain to spatiotemporal series files (.series) that were created with ENVI's Build Raster Series tool.

  • Regular Bands: A Boolean parameter that indicates if all rasters in a series have the same number of bands and the same band names. For example, this field is set to True if all rasters have three bands representing 400 nm, 500 nm, and 600 nm each. If it is False, the rasters in the series may differ by the number of bands or have different band names, making it more difficult to visually compare the images over time.
  • Regular Grid: A Boolean parameter that indicates whether or not all rasters in a series can be represented on a grid with a common spatial extent, pixel size, and coordinate system. If this field is set to False, each raster may have a different spatial extent or dimensions.

See Also


ENVI Header Files, Optional ENVI Header Fields, Edit Raster Metadata, Edit NITF Metadata, Supported Data Types, ENVIRasterMetadata (API), ENVIRaster::WriteMetadata (API)



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