ENVI Header Files

Data acquisition time string that conforms to the ISO-8601 standard. The string can be in any of the following formats:

YYYY-MM-DD

YYYY-MM-DDTHH:MM:SS.DZ

YYYY-MM-DDTHH:MM:SS:Dooo:mm

Where:

• YYYY is the four-digit year
• MM is the two-digit month
• DD is the two-digit day
• T separates the date and time
• HH is the two-digit hour
• MM is the two-digit minute
• SS is the two-digit second
• D is the decimal fraction of a second with up to double-precision
• Z indicates that the time is in Coordinate Universal Time (UTC)
• ooo is a two-digit offset in hours from UTC time. If the offset is negative, a minus symbol (-) precedes the value.
• mm is an optional partial-hour offset (in minutes) from UTC time.

The names of image bands.

The number of bands per image file.

Lists the bad band multiplier values of each band in an image, typically 0 for bad bands and 1 for good bands.

The order of the bytes in integer, long integer, 64-bit integer, unsigned 64-bit integer, floating point, double precision, and complex data types. Use one of the following:

• Byte order=0 (Host (Intel) in the Header Info dialog) is least significant byte first (LSF) data (DEC and MS-DOS systems).
• Byte order=1 (Network (IEEE) in the Header Info dialog) is most significant byte first (MSF) data (all other platforms).

Lists class colors using RGB color definitions for classification files. For example, black is 0,0,0.

Lists class names for classification files.

Defines the number of classes, including unclassified regions, for classification files.

Percentage of cloud cover within the raster.

Default color table to use when ENVI displays the image. This is stored as an array of 768 numbers of type byte, representing the 3 by 256 color table to use.

Specifies the values to calculate from a complex image and to use when displaying the image, calculating statistics for the image, or writing the image to a new file. Values include Real, Imaginary, Power, Magnitude, and Phase. The default value is Power.

When you save a georeferenced file to ENVI raster format, ENVI adds a coordinate system string field to the header file. It lists the parameters used for a geographic or projected coordinate system. Following are some examples:

A geographic coordinate system (for example, Geographic Lat/Lon) string contains the word GEOGCS and lists the coordinate system name, datum, spheroid, prime meridian, and units:

coordinate system string = 

GEOGCS["GCS_WGS_1984",

DATUM["D_WGS_1984",

SPHEROID["WGS_1984",6378137.0,298.257223563]],

PRIMEM["Greenwich",0.0],

UNIT["Degree",0.0174532925199433]]

A projected coordinate system string contains the word PROJCS and lists all of the geographic coordinate system parameters, plus detailed parameters that describe the projected coordinate system:

coordinate system string = 

PROJCS["WGS_1984_South_Georgia_Lambert",

GEOGCS["GCS_WGS_1984",

DATUM["D_WGS_1984",

SPHEROID["WGS_1984",6378137.0,298.257223563]],

PRIMEM["Greenwich",0.0],

UNIT["Degree",0.0174532925199433]],

PROJECTION["Lambert_Conformal_Conic"],

PARAMETER["False_Easting",0.0],

PARAMETER["False_Northing",0.0],

PARAMETER["Central_Meridian",-37.0],

PARAMETER["Standard_Parallel_1",-54.0],

PARAMETER["Standard_Parallel_2",-54.75],

PARAMETER["Latitude_Of_Origin",-55.0],

UNIT["Meter",1.0]]

See Coordinate System Strings and Codes for more information.

Gain values for each band. Units are W/(m2 * µm * sr).

Pixel values that should be ignored in image processing.

Offset values for each band.

An array of reflectance gain values.

With Landsat-8 files, the reflectance gains have been scaled by the sine of the sun elevation, as follows:

data reflectance gain values = REFLECTANCE_MULT_BAND_1/sin(sun elevation)

An array of reflectance offset values. With Landsat-8 files, the reflectance offsets have been scaled by the sine of the sun elevation, as follows:

data reflectance offset values = REFLECTANCE_ADD_BAND_1/sin(sun elevation)

The type of data representation:

• 1 = Byte: 8-bit unsigned integer
• 2 = Integer: 16-bit signed integer
• 3 = Long: 32-bit signed integer
• 4 = Floating-point: 32-bit single-precision
• 5 = Double-precision: 64-bit double-precision floating-point
• 6 = Complex: Real-imaginary pair of single-precision floating-point
• 9 = Double-precision complex: Real-imaginary pair of double precision floating-point
• 12 = Unsigned integer: 16-bit
• 13 = Unsigned long integer: 32-bit
• 14 = 64-bit long integer (signed)
• 15 = 64-bit unsigned long integer (unsigned)

Indicates which band numbers to automatically load into the Data Manager Greyscale or R, G, and B fields every time the file is opened. By default, a new image is automatically loaded when a file that has default bands defined in its header is opened. If only one band number is used, then ENVI loads a greyscale image.

The type of stretch to use when ENVI displays the image. The choices are as follows:

• bipolar
• equalization: You can optionally enter a minimum and maximum pixel value to use in the stretch. For multi-band images, these values will apply to all of the bands. You cannot set individual minimum/maximum values for each band. Here is an example: equalization 0 200.
• Gaussian: Optionally enter the standard deviation to use; for example: 0.3 Gaussian. You can optionally enter a minimum and maximum pixel value to use in the stretch. For multi-band images, these values will apply to all of the bands. You cannot set individual minimum/maximum values for each band. Here is an example: 0.3 Gaussian 0 1000.
• linear: Optionally specify the percentage of the data to clip; for example: 5.0 linear. Or, enter the minimum and maximum pixel values to use in the stretch; for example: 0 200 linear.
• logarithmic: You can optionally enter a minimum and maximum pixel value to use in the stretch. For multi-band images, these values will apply to all of the bands. You cannot set individual minimum/maximum values for each band. Here is an example: logarithmic 0 1000.
• optimized linear
• square root: Optionally enter the square root factor to use; for example: 0.5 square root. You can optionally enter a minimum and maximum pixel value to use in the stretch. For multi-band images, these values will apply to all of the bands. You cannot set individual minimum/maximum values for each band. Here is an example: 0.5 square root 0 200.

Path and filename of a DEM associated with the image.

A string describing the image or the processing performed.

The ENVI-defined file type, such as a certain data format and processing result. The string must exactly match an entry in the File Type drop-down list in the Edit ENVI Header dialog.

Lists full-width-half-maximum (FWHM) values of each band in an image. Units should be the same as those used for wavelength and set in the wavelength units parameter.

Geographic corners for non-georeferenced files. Enter one to four locations. Each location must contain the following items, in this order:

pixel_x_coordinate, pixel_y_coordinate, latitude, longitude

For example:

geo points = {

1.0000, 1.0000, 32.89380137, -117.07201460,

1002.0000, 1.0000, 32.87364744, -116.95855862,

1.0000, 1002.0000, 32.80628336, -117.09960891,

1002.0000, 1002.0000, 32.78615422, -116.98625969}

Pixel coordinates [1,1] correspond to the top-left corner of the image.

The number of bytes of embedded header information present in the file. ENVI skips these bytes when reading the file. The default value is 0 bytes.

Refers to whether the data interleave is BSQ, BIL, or BIP.

The number of lines per image for each band.

Lists geographic information in the following order:

• Projection name
• Reference (tie point) pixel x location (in file coordinates)
• Reference (tie point) pixel y location (in file coordinates)
• Pixel easting
• Pixel northing
• x pixel size
• y pixel size
• Projection zone (UTM only)
• North or South (UTM only)
• Datum
• Units

Indicates x and y pixel size in meters for non-georeferenced files.

If you defined a custom projection in ENVI Classic, this field contains that map information. A projection info line is added to the ENVI header file if the image uses a user-defined projection instead of a standard projection defined in the file map_proj.txt file of the ENVI distribution. If the header file contains a coordinate system string field, any existing projection info line information is ignored.

The names of spatial and spectral read routines used in ENVI Classic custom file readers.

The value that, when divided into your data, would scale it from 0-1 reflectance. For example, if the value of 10,000 in your data represents a reflectance value of 1.0, enter a reflectance scale factor of 10,000.

Lists Rational Polynomial Coefficient (RPC) geolocation information for files that have RPC reference information instead of a standard map projection.

The number of samples (pixels) per image line for each band.

Instrument types, such as Landsat TM, SPOT, RADARSAT, and so on. The string must exactly match an entry in the Sensor Type drop-down list in the Edit ENVI Header dialog.

Top of the atmosphere solar irradiance per band. Units are W/(m² * µm).

A comma-separated list of spectra names enclosed in {curly brackets}; for spectral library files only.

Angle of the sun (in degrees) from due north in a clockwise direction.

Angle of the sun (in degrees) above the horizon.

The timestamp names of temporal cube bands.

Lists the center wavelength values of each band in an image. Units should be the same as those used for the fwhm field and set in the wavelength units parameter.

Text string indicating the wavelength units. ENVI accepts the following strings:

Micrometers

um

Nanometers

nm

Millimeters

mm

Centimeters

cm

Meters

m

Wavenumber

Angstroms

GHz

MHz

Index

Unknown

Defines the image coordinates for the upper-left pixel in the image. Images that are spatial subsets of larger images often use an image coordinate system that references the parent (or larger) image so that you can link and dynamically overlay the two images. The default values for the upper-left pixel are (0,0).

The reference (tie point) pixels in the map info header field are one-based.

Changing these values does not affect the way ENVI reads the image data from the file.

The number of pixels in the x and y directions to average for Z plots.

The default minimum and maximum values for Z plots.