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: support-asdc@earthdata.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