I. EARTH LOCATION CORRECTION SUBROUTINE ELC:

The subroutine, ELC, was developed for NOAA by Dr. Seiichiro Kigawa, a visiting scientist
from the the Japan Meteorological Agency in Tokyo, Japan; to correct the AMSU-A earth
location using the appropriate attitude parameters.   This README file provides information
needed for the user to integrate subroutine ELC into their level 1B product processing.  

The ELC routine uses the latitudes and longitudes for each sample from two adjacent scan lines
and computes the satellite position and velocity vector.  These vectors are used to recompute the
latitude and longitude with the effect of the attitude corrections incorporated.  Geodetic latitude
and longitude are output to replace the original values.  Recommended values for the attitude
error are provided in a table on this website. 
 
1. Input to the subroutine ELC through the argument are:
     LAT0(30)  - the first scan line level 1B latitudes for each sample along the scan line in
     degrees 
     LON0(30)  - the first scan line level 1B longitudes for each sample along the scan line in
     degrees 
     LAT1(30)  - the second scan line level 1B latitudes for each sample along the scan line in
     degrees 
     LON1(30)  - the second scan line level 1B longitude for each sample along the scan line
     in degrees 
     ROLL(30)   - Roll errors in radians      
     PITCH(30)  - Pitch errors in radians 
     YAW(30)    - Yaw errors in radians 
     OFFSET =0, LATC and LONC are corrected data of LAT0. LON0
            =1, LATC and LONC are corrected data of LAT1. LON1
  
     Input to the routines requires two consecutive scan lines. The LAT0, LON0 are the
     latitudes and longitudes of the 30 scan points for the first scan line, while the LAT1,
     LON1 are for the second scan line.  The ROLL, PITCH, YAW are the attitude corrections
     for each scan point. 

 2. Output from the routine ELC through the argument are:
     LATC(30)  [radians]
     LONC(30)  [radians]


II. TEST PROGRAM AND TEST DATA:

A test program to read and correct AMSU-A level 1B data using the input attitude corrections 
through the input  namelist RPYCO is provided to aid in your testing and implementation. Test 
data is also provided. 

Input to the test program is the operational level 1B data. There is a yaw=0.2 degree of 
spacecraft attitude correction applied in the operational level 1B data. In the test program 
only roll and pitch corrections are applied. The corrected level 1B data output from the test 
program then should have the roll, pitch and yaw corrections.

The following namelists are used in the test program (in degree):  

1. AMSU-A2 (Ch 1-2) 
 &RPYCOR ROLLD = 30*-1.03                                              
 PITCHD= 30*+0.18                                                      
 YAWD =  30*0.0,  &END                                                 
                                                                    
2. AMSU-A1-2 (Ch 3-5, 8)
 &RPYCOR ROLLD = 30*-0.218                                             
 PITCHD= 30*+0.315                                                     
 YAWD =  30*0.0,  &END 

3. AMSU-A1-1 (Ch 6-7, 9-15)
 &RPYCOR ROLLD = 30*-0.218                                             
 PITCHD= 30*+0.349                                                     
 YAWD =  30*0.0,  &END 

The following datasets are the input and output level 1B test data. The earth location information 
is generated by the IPD AELDS system (normal operations) and by the S. Kigava's ELC routine. 
Output data is provided for you to compare your results once you implement the ELC routine.

1. Operational level 1B (Input)
     Name: AMAX.NK.D03058.S1115.E1300.OPS (by AELDS)
     Attitude corrections:
                   Roll=0.0 deg.
                   Pitch=0.0 deg.
                   Yaw=0.2 deg.
 
2. For AMSU-A2 (Ch 1-2) correction (Output)
    Level 1B data names:
             AMAX.NK.D03058.S1115.E1300.AA2 (by AELDS)
             AMAX.NK.D03058.S1115.AA2.ELC (by ELC)
    Attitude corrections:
                   Roll=-1.03 deg.
                   Pitch=0.18 deg.
                   Yaw=0.2 deg.
    Output from test driver for ELC: NKA2OUT.txt
 
3. AMSU-A1-2 (Ch 3-5, 8) correction (Output)
    Level 1B datanames:
           AMAX.NK.D03058.S1115.E1300.A12 (by AELDS)
           AMAX.NK.D03058.S1115.A12.ELC (by ELC)
    Attitude corrections:
                   Roll=-0.218 deg.
                   Pitch=0.315 deg.
                   Yaw=0.2 deg.
    Output from test driver for ELC: NKA12OUT.txt 

4. For AMSU-A1-1 (Ch 6-7, 9-15) correction (Output)
    Level 1B datanames:
            AMAX.NK.D03058.S1115.E1300.A11 (by AELDS)
            AMAX.NK.D03058.S1115.A11.ELC (by ELC)
    Attitude corrections:
                   Roll=-0.218 deg.
                   Pitch=0.349 deg.
                   Yaw=0.2 deg.
    Output from test driver for ELC: NKA11OUT.txt

The sample program is to use S.Kigava's routine ELC to perform the attitude correction.