LMD - November , 1995
A2 contains data for one day ( zero to 24 UT ) and one satellite. Each record contains data for 48 seconds or 8 scans or 408 pixel measurements. Index Quantity Unit Bits Scale f. Offset 1 Julian Date ( whole part ) day 32 1 0 2 Julian Date ( fractional part ) day 32 1000000000 0 3 Earth-Sun Distance AU 32 1000000000 0 4-5 Satellite Position, X m 32 1 0 6-7 Satellite Position, Y m 32 1 0 8-9 Satellite Position, Z m 32 1 0 10-11 Satellite Velocity, X m/s 32 1 0 12-13 Satellite Velocity, X m/s 32 1 0 14-15 Satellite Velocity, X m/s 32 1 0 16-17 Satellite Nadir, Colatitude deg 16 100 0 18-19 Satellite Nadir, Longitude deg 16 100 -180 20 Sun Position, Colatitude deg 16 100 0 21 Sun Position, Latitude deg 16 100 -180 22 Orbit Number ---- 16 1 0 23-430 Pixel, Colatitude deg 408*16 100 0 431-838 Pixel, Longitude deg 408*16 100 -180 839-1246 Filtered Radiance, Total W m-2 sr-1 408*16 10 0 1247-1654 Filtered Radiance, SW W m-2 sr-1 408*16 10 0 1655-2062 Filtered Radiance, Vis W m-2 sr-1 408*16 100 0 2063-2470 Filtered Radiance, IR W m-2 sr-1 408*16 100 0 2471-2878 Viewing Zenith Angle deg 408*16 100 0 2879-3286 Solar Zenith Angle deg 408*16 100 0 3287-3694 Relative Azimuth deg 408*16 100 -180 3695-3696 A' Coefficient ---- 2*16 1000 0 3697-3744 Quality Index ---- 48*8 1 0 3745 Full Record Index ---- 1*8 1 0 3746-3747 Calibration Reference ---- 1*8 1 0 3748-3951 Spare ---- 204*8 3952-4359 Unfiltered Radiance, SW W m-2 sr-1 408*16 10 0 4360-4767 Unfiltered Radiance, LW W m-2 sr-1 408*16 10 0 4768-5175 Outgoing Flux, SW W m-2 408*16 10 0 5176-5583 Outgoing Flux, LW W m-2 408*16 10 0 5584-5991 Identified Scene Type ---- 408*8 10 0 5592-6002 Spare ---- 11*8 Total 11360*8 Bits
A2 contains data for one day ( zero to 24 UT ) and one satellite and is equivalent to ERBE S8, except the lack of Wide FOV and Medium FOV data.
Whole part of the Julian Date at the beginning of the record.
Fractional part of the Julian Date at the beginning of the record.
Comments on A2(1) and A2(2) : The same date as ERBE is used and provides a continuous time record useful in the processing of regional means. The Julian date is the universal reference to date astronomical events. Its origin is : January 1st 4717 B.C at noon (UT)
Examples : A2(1) A2(2) Calendar date UT 2432 550 0.5 JAN 02 1948 00:00:00 2444 000 0.0 MAY 23 1968 12:00:00 2445 000 0.0 OCT 09 1995 12:00:00 2451 544 0.5 JAN 01 2000 00:00:00
in astronomical unit ( 0.98 < A2(3) < 1.02 )
Comments on A2(4....9) :
The unit is : meter. They are relative to the Earth coordinate system defined from:
origin : earth centre X,Y plane : equator plane OX axe: Greenwich longitude
These positions are used to compute the view angles of the target point A2(2471..3694).
Comments on A2(10...15) :
The unit is : meter/second . Same coordinate system.
These elements are only necessary to interpolate X,Y,Z inside the record period, when the view angles are computed with a better accuracy.
Comments on A2 (16..21) : all in decimal degrees and correspond to same coordinate system as the preceding values
Relative number. Its origin should be close to the first real satellite orbit. It increases by 1 at the ascending node. Although not directly used in the secondary processing, this element is a practical index used in any satellite data comparisons. It is also useful to show the spatial coverage of one orbit without any overlap from another orbit.
Comments : borrowed from the "remote sensing" terminology, pixel stands for the elementary target viewed from the satellite. These colatitude and longitude correspond to the centre of pixel, i-e the point where the sensor's optical axis intercepts the 30 km altitude earth envelop (top of the atmosphere for the ERB study ). They are computed at the level 1 data processing, with orbit bulletin updated every 15 days. The accuracy is assumed to be the half-pixel, i.e. 30 km or 0.3 degree at the equator. Both colatitude and longitude are in decimal degrees and corresponds to the same coordinate system as the preceding elements
in W m-2 sr -1 - Raw measurement of channel 3 after count conversion.
in W m-2 sr -1 - Raw measurement of channel 2 after count conversion.
in W m-2 sr -1 - Raw measurement of channel 1 after count conversion.
in W m-2 sr -1 - Raw measurement of channel 4 after count conversion.
Relative azimuth between the solar plane and the viewing plane. Zero in the forwards plane.
Comments : these 3 angles (in degree ) are relative to the local ( or pixel ) coordinate system defined as following :
origin : pixel centre oz : vertical ox :solar plane
They are computed at the centre of each pixels. This centre is located at an altitude of 30 km, above the Earth's surface defined by an ellipsoid of 6378.160 km and 6356.775 km, respectively for the equatorial and polar axis.
In the initial design, this coefficient had to be adjusted for calibration variations over short periods of time. For ScaRaB flight model 1, it is now assumed constant and equal to 0.845
Due to change in the SW calibration method, most flags are pointed to 'substitution' and have a very low significance. All data for radiances and angles may be used, except if they have default value.
equal to 'one' if the second half of the record is missing. No significance for the users since the concerned data are set to default value.
This number refers to the job used to generate the calibration sets. Low significance for the users
in W m-2 sr -1 Correction for underestimation at the shortest wavelengths, domain where the instrument response diminishes.
in W m-2 sr -1 Subtraction of the SW unfiltered radiance from the Total unfiltered radiance. SW unfiltered radiance is weighted by coefficient A'.
in W m-2 The SW unfiltered radiance is converted into flux, using the view and sun angles, the scene identification and the SW Erbe bi-directional function ( Suttles et al, 1988). A linear interpolation of BRDF between angles is used in order to remove the discrete nature of the angular model TOA : top of atmosphere (30km altitude as in Erbe)
in W m-2 . The LW unfiltered radiance is converted into flux, using the view angle and colatitude, the scene identification and the LW Erbe anisotropic function ( Suttles et al, 1988). A linear interpolation of the anisotropic function between view angle and colatitude is also used.
There are 13 possible values for the whole part
o unknown scene 1 .. 12 combination of 5 geotypes and 4 cloud category 127 default value.
As in Erbe S8 format, the decimal part gives the data input of the geotype ( from 0 to 4 )