FIRE_ETO_UTAH_PDL README

This is the readme file for the FARS(Facility for Atmospheric Remote Sensing)
Ruby Lidar ETO data set. For further information please contact:

        Langley DAAC Science, User and Data Services
        Mail Stop 157D
        2 South Wright St.
        NASA Langley Research Center
        Hampton, VA 23681
        email: larc@eos.nasa.gov
        Phone: (757)864-8656
        FAX: (757)864-8807

Location:
	Salt Lake City, Utah
	Latitude: 40 46' 00' N
	Longitude: 111 49' 38'' E
	Elevation: 1520 meters above sea level

Instrument:

	Ground based Polarization Cloud Ruby LIDAR

Specifications:

	2 channels
	vertical polarization transmitted
	manually "tiltable" +/- 5 degrees from zenith
	0.1 Hz PRF, 7.5 meter maximum range resolution
	1-3 mrad receiver beamwidths
	25 cm diameter telescope
	0.694 micron wavelength

Operating Procedure and Measurements:

	Data is recorded with the FARS Ruby LIDAR system when cirrus clouds 
are present overhead.  Observations usually begin several minutes before the 
cirrus arrives and is concluded several minutes after the cirrus passes.  Data 
collection normally occurs in periods of 1-3-h in support of the local overpass 
times of polar-orbiting satellites.  The LIDAR is primarily operated in the 
zenith direction.  When conditions are suitable, the instrument is tilted +/- 5
degrees off the zenith to test for horizontally oriented plate crystals.  Raw 
LIDAR backscattered return is recorded for 2 channels containing parallel and 
orthogonal polarized signals.  The time is recorded in Universal Time 
Coordinate (UTC).

Data Processing:

	Raw LIDAR backscattered return has been processed using system 
constants to calculate LIDAR relative returned parallel polarized signal 
(backscatter).  The vertical resolution has been averaged from 7.5 meter to 75 
meter resolution.  The original data set is recorded at a maximum resolution of 
0.1 Hz PRF (1 shot per 10 seconds). This data set has been averaged to 2 
minute intervals to provide higher accuracy, reduce noise, and to minimize disk 
space requirements needed to work with the data set.  If higher resolution data 
is needed, please contact the person listed below.  The data set was searched 
for data recording errors (explained below), and these errors were removed 
from the 2 minute average.

Data Recording Errors:

	Three types of checks were performed to remove data recording errors 
and assure data quality.  

I.  Background checks - The background is a prepulse that is fired before the 
	main LIDAR signal pulse.  The raw background signal is a number between 
	-128 and +127 and consists of 100 points.  Three types of background
	checks are performed.

	A.  Offscale setting - If more than 5 background points are equal to
	-128 or more than 5 points equal to +127, the signal is considered
	offscale and the shot is rejected.

	B.  Pretrigger - An average of every 10 background points, up to 80 
	points, is calculated.  If the largest average value is greater than or
	equal to 1.1 times the smallest average, the shot is rejected.

	C.  Noisy signal - The standard deviation of the first 75 background
	points is calculated.  If the standard deviation is greater than 10.0,
	the shot is rejected.

II.  Signal checks - Sometimes there are errors in the signal that are not 
		detected in the background checks.

	A.  No data recorded - The standard deviation of the entire signal is 
	calculated.  If the standard deviation is less than 1.0, the shot is
	rejected.

	B.  Oscilloscope false trigger - This error is detected by finding a 
	fluctuating signal in the first 10 to 20 points of the LIDAR profile. 
	If the signal oscillates several times between positive and negative
	values and then becomes a straight line, the shot is rejected.

III.  LIDAR system checks

	A.  Valid power out - If the recorded laser power output is less than
	0.5 Joules the shot is rejected. 

	B.  Valid photo-multiplier tube (PMT) - If the PMT voltage is less than
	0.5 Joules the shot is rejected.

Data Format:

	The data set consists of 590 ASCII data files arranged in chronological 
order. The file names reflect the date and start and stop times for each file. 
An example of a file name is:  
		rb92_01010000_0100.2min
		rbYY_MMDDH1M1_H2M2.2min
where 		YY: year
	        MM: month
	       	DD: day
	       	H1M1: hour and minute of start time
	       	H2M2: hour and minute of stop time
		
Each file contains 2 minute averages of LIDAR relative returned backscatter 
signal at 75 meter resolution. The time is recorded in UTC.  The format (in 
ASCII) of each LIDAR shot is:

		year month day hour minute second  (start time of average)
		year month day hour minute second  (end time of average)
		shot_avg   total_shots   n_vertical
		n_angle
		parallel_polarized_data (n_vertical points)

where 	shot_avg:  number of shots in the 2 minute average
		total_shots:  total number of shots tested for errors in the 2
			minute interval
		n_vertical:  number of points in the vertical
		n_angle:  number of points in average where the LIDAR axis is 	
			tilted off the zenith
		parallel_polarized_data:  n_vertical points of data where the
			first point is 75 meters above ground level (AGL) and
			the vertical resolution is 75 meters, or since the site
			is 1520 meters above sea level, the first data point
			would be 1595 meters Mean Sea Level (MSL).

An example of 1 LIDAR shot, including the header information is:

   92  3  12  19  13  0
   92  3  12  19  14  48
   10  10  143
   0
   357  357  357  357  357  357  357  357  357  357  357  357  357  356  337
   295  232  168  147  129  115  103  94  85  78  72  67  62  58  53  56  58  54
   51  48  46  44  41  39  36  35  32  31  29  28  25  23  22  21  20  19  17
   16  16  15  13  13  12  12  11  11  10  10  10  9  9  9  8  8  8  7  7  7  7
   7  6  6  6  6  6  5  5  5  5  5  5  4  4  4  4  4  4  4  4  4  4  3  3  3  3
   3  3  3  3  3  3  3  3  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  8  2
   2  2  2  1  1  1  2  2  1  1  1  2  2  2  1  1  1

Data set point of contact:

   Name: 	Jennifer Barnett
   Address: 	University of Utah
	    	135 South 1460 East Rm. 819
	    	Salt Lake City UT 84112-0110
   Telephone: 	801-585-9491
   Fax: 	801-585-3681
   Internet Address: jbarnett@atmos.met.utah.edu