A data acquisition system (DAS) for the NASA/LaRC Differential Absorption Lidar (DIAL) was documented. This DAS is a dual LSI 11/23 set up where one computer retrieves data from the digitizers and other peripheral units, stores that data on magnetic tape, generates aerosol grayscales on a Trilog printer and passes data to the second computer. The second computer is dedicated to real time displays of the data in a variety of modes from raw data to range resolved ozone profiles. The DIAL DAS also has several new features

Butler, C.

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DEPARTMENT OF GEOLOGY
SCHOOL OF SCIENCES AND HEALTH PROFESSIONS
OLD DOMINION UNIVERSITY
NORFOLK, VIRGINIA
TZCHNIC.AL REPORT GSTR-84-12
FIELD TES'S OF THE REAL-DATA f 4
m ACQUISITION SYSTEM FOR THE NASA-LaRC
i	 "44P DIFFERENTIAL ABSORPTION LIDARin
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Carolyn Butler
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Submitted by Earl C. Kindle, Principal 	 Investigator
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P.O. Box 6369
wet Norfolk, Virginia 23808 ,
September 1984
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A data acquisition system (DAB) for the NASA/LaRC
Differential Absorption Lidar (DIAL) was documented n ODU
Technical Report GSTR-84-5. This DAB is a dual LSI 11!23 set-up
where one computer retrieves data from the digitizers and other
peripheral units, starers that data on magnetic tape, generates
aerosol grayscales on a Trilog printer and passes data to the
second computer. The second computer is dedicated to real-time
displays of the data in a variety of modes from raw data to range
resolved ozone profiles. The DIAL DAB also has several new
features:
(1) a dual mag tape drive system whi ct al l ov s for
continuous data acquisition during rewind operations
(2) both tape units can record in streamer mode (100 ips)
if the data is buffered appropriately
(3) five new Transiac 12-bit digitizers and amplifiers to
replace the Biomation 10-bit digitizers
(4) a Matrox @RGB-GRAPH Controller for video display with
256 X 512 pixel resolution
(5) a navigation interface which accepts both LORAN and
- OMEGA inputs (switch selectable) for latitude and
longitude data
(6) a ADV11-C analog to digital converter with up to 10
volt range for digitization of laser energies and met
data
(7) a TCU50-DYR time clock with capability to retain time
of day and date for upto 3 months without external power
In order to implement these system improvements the DIAL DAB
software had to be, for the most part, re-designed. I have
written all my own MACRO subroutines to drive each of these
peripheral units in order to save CPU time and memory and to
customize them for our purposes. The resulting MASTER program
which runs on LSI #1 uses nearly all of the 128k word memory
available. The MASTER program and RT-11 monitor reside in the
lower 32k of memory. Extended memory is used for data storage
from the Transiacs (up to 4096 words per buffer) where it is
buffered until written to magnetic tape. The SLAVE program which
runs on LSI #2 uses only the lower 32k of memory.
The DIAL DAB hardware and software were first field tested
in April 1984 during the Global Tropospheric Experiment's (GTE)
Tropopause Fold Experiment (TPE).	 The TPE is one of a number of
experimental objectives of the GTE.
	 The TFE was conducted to
measure the effects of a stratospheric incursion into the trop-
osphere.	 On a number of different flights the NASA Electra flew
across the fold. The DIAL system made simultaneous measurements
of aerosols and ozone with dramatic increases of both species
observed in the fold itself.
The DIAL DAB proved not only flight worthy but also did
nearly everything it was designed to do. The problems
encountered are outlined below.
(1) Due to the use of re-cycled tapes, dirt collected on
the head of one of the Cipher tape drives which left
us with only one tape drive for the remainder of the
flight.	 The	 tape	 drives are
	
not	 easily	 accessible
during	 flight	 so	 we were forced to	 circle	 back	 to
position during rewind operations.	 This problem	 was a
avoided on future flights by periodic cleaning of 	 both
tape units and
	
by using only new tapes.
(2) One of the Transiac units overheated minutes after 	 the
CAMAC
	
crate	 power was turned on but since we	 carried
spares	 this	 did	 not present a	 major	 problem.	 The
problem	 turned out to be a temperature sensor 	 on	 the
unit	 that	 was bent too close to a very	 active,	 heat
generating	 component.	 The sensor was bent in	 anoiher
direction and the problem went away.
(3) To allow for more cooling to occur in the Transiacs all
the	 sides	 were	 removed	 from	 the	 amplifiers	 and
digitizers.	 On	 later	 analysis	 of	 the	 data,
discontinuties	 were found in the returns which 	 turned
out to be caused by "cross-trlk" between amplifiers and
the	 digitizers.	 The sides were all replaced and	 the
problem was eliminated.
(4) The	 software was written so that the highest 	 priority
was	 to	 record
	
the data on	 tape.	 During	 the	 TFE,_
however, CPU scheduling conflicts occurred occasionally
between the mag tape interface (DILOG D0130), formatted
Fortran	 WRITE
	
instructions to the Trilog	 T-100	 and
data	 transfer	 from
	
the Transiacs.	 The problem
	
was
minimized during	 the	 experiment by starting output to
the printer	 (which begins	 with a	 For*ren	 WRITE then
proceeds to plot output) prior to 	 recording data.	 On
return
	
to	 Langley,	 the	 D` I ZC	 interface 	 board	 was
modified	 to	 make it	 a	 high	 priority	 device.	 The
harjware	 modification now allows the mag tape routines
to interrupt the Transiac data_transfer routines. Since
I	 have	 no	 control over the	 priority status	 of	 the =
Fortran WRITE statements a timing conflict occasionally`
occurs.	 This	 timing	 conflict results in the loss of,__
at most, 20 data shots before the problem is
	
corrected
and only occurs when the banner record (256 word record`
printed	 at	 start	 of grayscales) is	 printed	 on	 the -a
Trilog -- if it happens at all.
(5) A software bug caused
	
LSI X11 to	 fail	 intermittently.
Attempts were
	 made to trace the bug in between flights
but	 to no avail.
	 During flights the solution to such
failures was to re-start both computers.	 On return	 to
Langley the error was eventuallly found and corrected.
During the months of May and June items (3), (4) and (5)
above were corrected.
	 Additional hard copy aerosol grayscales
with profile averaging were generated. An option to average upto
	
is
15 shots for the aerosol grayscales, in flight, was added to the
program.
	 An array transformation for a log amplifier was
included in the program (but never implemented in the field).	 i
More versatility in choosing the area for background subtraction
was incorporated into the program with the command BGLEN I where
I is the number of words to average (see SSIR-84- 5 p.42).
By early June DIAL was back in the field preparing for
2
r .
another GTE project.
	 The Atlantic Boundary Layer Experiment
(ABLE) was designed to study the marine boundary layer off the
continental shelf.	 For two • jeeks flights were made over
Barbados, W.I. with the DIAL system again measuring ozone and
aerosols.	 One flight was made over Guyana to study the
atmosphere over the dense tropical rain forests.
	 This latter
flight was a feasibility study for next year's mission to Brazil.
The DIAL DAS functioned extremely well -- the hardware worked
	 {
reliably; the software did all it was designed to do with no
"bugs"
IN
3


Field tests of the real-data acquisiton system for the NASA-LaRC differential absorption lidar

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