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.