NASA ASTER Level 1T Data Dictionary

 

 

Acquisition Date

• Field Definition:  The date the data was acquired.

               Format:
               YYYY/MM/DD
 

Acquisition Time

• Field Definition:  The time the data was acquired.

               Example:
               18:25:28.354

Band Available

• Field Definition:  ASTER L1T can include up to three Visible and Near Infrared (VNIR) bands, six Shortwave Infrared (SWIR) bands, and five Thermal Infrared (TIR) bands. The Band Available flag indicated if the band is available for the scene.
   

Cloud Cover

• Field Definition:  Cloud Cover is the percentage of a full scene that is obscured by clouds and is the average of all four quadrant cloud cover values.
  
    Values:
    0 - 100
   

Coordinates Decimal Degrees

• Field Definition:  The latitude and longitude are provided in decimal degrees for the following fields:

                 Values:      
                 Scene Center Latitude and Longitude
                 Northeast (NE) Corner Latitude and Longitude
                 Northwest (NW) Corner Latitude and Longitude
                 Southeast (SE) Corner Latitude and Longitude
                 Southwest (SW) Corner Latitude and Longitude

                 Latitude Format Decimal Degrees: -90.000 through 90.000
                 Longitude Format Decimal Degrees: -180.000 through 180.000

                 Number of decimal places will vary by dataset – check collection in EE.
 

Coordinates Degrees, Minutes, Seconds

• Field Definition:  The latitude and longitude are provided in degrees, minutes, and seconds for the following fields:

                 Values:
                 Scene Center Latitude and Longitude
                 Northeast (NE) Corner Latitude and Longitude
                 Northwest (NW) Corner Latitude and Longitude
                 Southeast (SE) Corner Latitude and Longitude
                 Southwest (SW) Corner Latitude and Longitude

                Longitude Format:
                DDDMMSS.SSH
                DDD = Degree(s) with a range of 0 through 180
                MM = Minute(s) with a range of 0 through 59
                SS.SS = Second(s) with a range of 0 through 59.99
                H = Hemisphere with E for east and W for west

                Latitude Format:
                DDMMSS.SSH
                DD = Degree(s) with a range of 0 through 90
                MM = Minutes(s) with a range of 0 through 59
                SS.SS = Second(s) with a range of 0 through 59.99
                H = Hemisphere with N for north and S for south
 

Correction Achieved

• Field Definition:  The metadata field that contains the level of topographic correction achieved for an associated AST_L1T scene. The possible levels of correction include: "Terrain+Precision", “Terrain+Systematic”, “Precision”, or “Systematic”.
   

Date Entered

• Field Definition:  The date the granule was entered into the EarthExlorer database.

               Values:
               YYYY/MM/DD
 

Date Updated

• Field Definition:  The Date Updated refers to the date the inventory record was last updated in the EarthExplorer database.

               Values:
               YYYY/MM/DD
 

Day/Night

• Field Definition:  This field indicates whether the data was collected during the day or night. If a collection granule is acquired along the day/night terminator line (sunrise or sunset), it is declared as "Both".

               Values:
               Day
               Night
               Both
               All (Includes Day, Night, and Both)
 

Entity ID

• Field Definition:  This field uniquely identifies the individual Aster Level 1T scene.
   

Local Granule ID

• Field Definition:  The name of an individual file provided by LP DAAC.

               Format:
               PPP_PPP_VVVDDMMYYYYhhmmss_YYYYDDMMhhmmss_NNNNN
               PPP_PPP = Data Set Short Name (AST_L1T)
               VVV = Version number
               DDMMYYYY = Day, Month, and Year of Acquisition
               hhmmss = Acquisition time in Hours, Minutes, and Seconds
               YYYYDDMM = Year, Day, and Month of Production
               hhmmss = Production time in Hours, Minutes, and Seconds
               NNNNN = Random Processing Number

               Example: AST_L1T_00308122020232256_20200813114317_28418
 

Lower Left Quad Cloud Cover

• Field Definition:  Percent cloud coverage in the lower left quadrant of the scene.

               Values:
                0 - 100
 

Lower Right Quad Cloud Cover

• Field Definition:  Percent cloud coverage in the lower right quadrant of the scene.

               Values:
               0 - 100
 

Orbit Direction

• Field Definition:  The Orbit Direction indicates if the satellite is traveling in an ascending or descending pass.

               Values:
               AS = Ascending
               DE = Descending
 

Precision Correction

• Field Definition:  Correction is applied to all daytime AST_L1A input scenes where correlation statistics reach a minimum threshold, but there is no corresponding terrain data.
   

Processing Level

• Field Definition:  ASTER Level 1T data are radiometric, geometric, plus Terrain corrected.
   

Sun Azimuth

• Field Definition:  The Sun azimuth angle at the WRS scene center. Azimuth is the angle of horizonal deviation, measured clockwise from the north.
   

Sun Elevation

• Field Definition:  The Sun elevation angle at the WRS scene center. Elevation is the angle of vertical deviation from the tangent to the earth's surface to the line between the sun's center and the scene center point.
   

SWIR Mode

• Field Definition:  The Short Wave Infrared Radiometer (SWIR) is an advanced high resolution multispectral radiometer which detects reflected solar radiation from the earth surface in the wavelength region of 1.6 - 2.43 um. SWIR also has the capability to change the boresight in the cross-track direction by +/-8.55 degrees from nadir, by using a pointing mechanism.

               Values:
               ON = SWIR mode on
               OFF = SWIR mode off
 

Systematic Correction

• Field Definition:  Correction is applied to all AST_L1A input scenes when the correlation statistics do not reach the minimum threshold and there is no corresponding terrain data. This level of correction is essentially an AST_L1B that has been rotated to a north-up map projection.
   

Terrain+Precision Correction

• Field Definition:  The highest level of correction achieved; applicable to all daytime AST_L1A input scenes where correlation statistics reach a minimum threshold.
   

Terrain+Systematic Correction

• Field Definition:  Correction is applied to AST_L1A input data for which the terrain+precision correction is not possible, usually because of poor ground imaging (e.g., heavily-clouded scenes, night scenes, TIR only scenes) or where ground control is not available.
   

TIR Mode

• Field Definition:  The Thermal Infrared Radiometer (TIR) s an advanced spaceborne radiometer with five spectral bands in the thermal infrared (8-12 um). Its ability to measure thermal emission properties is useful for locating mineral resources, characterizing the land and sea surface and observing the atmosphere.

               Values:
               ON = TIR mode on
               OFF = TIR mode off
 

TIR P Angle

• Field Definition:  The Thermal Infrared Radiometer (TIR) P Angle refers to the pointing angle of the TIR subsystem. The scanning mirror functions both for scanning and cross-track pointing (to +/- 8.55 degrees). In the scanning mode, the mirror oscillates at about 7 Hz and, during oscillation, data are collected in one direction only. During calibration, the scanning mirror rotates 90 degrees from the nadir position to view an internal black body. Because of the instrument's high data rate, restrictions have been imposed so that the average data rate is manageable by the spacecraft data management system. This restriction is a one-orbit maximum average rate of 16.6 Mbps and a two-orbit maximum average rate of 8.3 Mbps, which results in approximately a 9.3% duty cycle.
   

VNIR1 Mode

• Field Definition:  This VNIR subsystem backward looking telescope is of the same design as the nadir telescope and contains only a single silicon charge coupled detector line array and no calibration lamps as it is only used to acquire a stereo pair image.

               Values:
               ON = VNIR1 mode on
               OFF = VNIR1 mode off
 

VNIR2 Mode

• Field Definition:  This VNIR subsystem nadir looking telescope is a reflecting-refracting improved Schmidt design. The focal plane of this telescope contains three 5000 silicon charge coupled detector line arrays.

               Values:
               ON = VNIR2 mode on
               OFF = VNIR2 mode off
 

VNIR P Angle

• Field Definition:  The Visible and Near-Infrared Radiometer (VNIR) P Angle refers to the pointing angle of the VNIR subsystem. The nadir and backward looking telescope pair are used for same orbit stereo imaging and can be rotated as a unit +/- 24 degrees to provide extensive cross-track pointing capability. Light from either of two halogen lamps are used periodically for subsystem calibration.
   

Upper Left Quad Cloud Cover

• Field Definition:  Percent cloud cover in the upper left quadrant of the scene.

               Values:
               0 - 100
 

Upper Right Quad Cloud Cover

• Field Definition:  Percent cloud coverage in the upper right quadrant of the scene.

               Values:
               0 - 100
 

WRS Path

• Field Definition:  The Worldwide Reference System 2 (WRS-2) path number associated with the scene.

               Values:
               001 through 233
 

WRS Row

• Field Definition:  The Worldwide Reference System 2 (WRS-2) row number associated with the scene.

               Values:
                001 through 244