United States
Environmental Protection
Agency
s>"
Atmospheric Sciences ;
Research Laboratory ~*f., «
Research Triangle Park. NC 27711 / /,"-
Research and Development
EPA/600/S3-88/015 May 1988
Project Summary
Development of an Adjustable
Buoyancy Balloon Tracer of
Atmospheric Motion: Phase III.
Refinement of the Operational
Prototype System
B. D. Zak and E. W. Lichfield
The adjustable buoyancy balloon
tracer of atmospheric motion is a
research tool designed to follow
atmospheric flows in both the
horizontal and the vertical, including
the weak sustained vertical motion
associated with meso- and
synoptic-scale atmospheric
disturbances. The design goals for
the tracer balloon specify a lifetime
> 3 days, tracking range > 1000 km,
ceiling altitude > 5.5 km (500 mb),
and capability to respond to mean
vertical flows as low as 1 cm/s. While
the tracer has applications
throughout the atmospheric
sciences, the immediate motivations
for this effort are to meet the need to
evaluate the accuracies of air
pollution transport models, to
establish source-receptor
relationships to distances of the
order of 1000 km, and to assess the
inherent limits on the predictability of
source impacts at long distances. In
Phase I of this project, entitled
"Systems Design and Demonstration
of Feasibility," the authors proposed
a generic design for such a system,
subjected the design to theoretical
analysis, constructed a test-bed
prototype, and conducted a series of
tests with that prototype to evaluate
the concept. In Phase II of the
project, the authors developed an
operational prototype designed to
meet the desired specifications. A
limited number of test flights of the
operational prototype were
conducted. Flights were made using
each of the three currently available
control algorithms: constant
pressure, constant potential
temperature, and zero relative
motion. Analysis of the data indicated
that, in each case, the control system
functioned properly. In Phase III of
the project, the subject of this
summary, improvements were made
in electronic design, packaging, and
in the remote command and data
reception system. Two test flights
were made, and while the results
from these flights were inadequate to
demonstrate that the design goals
were met, the results were not
inconsistent with that conclusion.
This Project Summary was
developed by EPA's Atmospheric
Sciences Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
The adjustable buoyancy balloon
tracer of atmospheric motion is a
physical Lagrangian tracer (PLT) - an
airborne instrumentation system that
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follows the flow of air in its vicinity, and
that can be tracked electronically. For
decades, researchers have sought such
a tracer to aid in understanding the
dynamics of the atmosphere: and more
recently, to cast light on long-range air
pollution: acid deposition, regional haze
and oxidant episodes, and associated
ecological effects. Advances in
microelectronics, satellite com-
munications, and battery technology
have now made a PLT system feasible.
The present effort is motivated primarily
by the immediate programmatic
requirements of the U.S. Environmental
Protection Agency. In a more basic
sense, however, it addresses a broad
underlying need for a convenient means
of following atmospheric flows.
PLTs are necessarily balloon-borne
systems and, consequently, must
operate under Federal Aviation
Regulations Part 101: Moored Balloons,
Kites, Vlnmanned Rockets, and
Unmanned Free Balloons. The purpose
of this regulation is to strictly limit the
hazard ^o air navigation that such
systems might otherwise represent. FAR
101 divides balloons into two classes.
Those that offer little hazard to aircraft
because of their limited size, weight, and
density are explicitly exempted from
most of the other stipulations of the
regulation. Under this provision, the U.S.
weather services, together with the
weather services of other nations around
the world, routinely launch hundreds of
radiosonde balloons twice daily.
Radiosondes measure the meteorological
conditions aloft from the surface to
beyond 20 km above many major
airports and certain other selected sites.
Balloons not satisfying the exemption
provisions of FAR 101 are treated much
like other aircraft, and are subject to strict
regulation.
It is an explicit design goal that the
tracer balloon operate under the
exemption clauses of FAR 101, as do
radiosondes. If this goal were not met,
FAR 101 would severely limit the
usefulness of the tracer balloon.
Because safety is a major
consideration, certain safety features
beyond those specified by FAR 101 are
incorporated in the tracer balloon design.
In particular, even though the Federal
Aviation Administration (FAA) does not
require it, when the tracer balloon is
flown at altitudes available to other
aircraft, it will carry an FAA transponder.
Consequently, the FAA will see the tracer
on radar as prominently as a commercial
airliner, and can control air traffic
accordingly.
The intended uses also provide other
tracer balloon design goals:
Lifetime > 3 days.
Tracking range > 1000 km.
Telemetry of relative vertical air
motion, pressure, temperature and
humidity.
Ground system capable of handling
several tracer balloons at a time.
Capable of establishing specified
ascent and descent rates under
radio command.
Capable of reaching altitudes up to
5.5 km (500 mb).
Capable of following mean vertical
flows as low as 1 cm/s with
acceptable fidelity.
Sufficiently inexpensive to permit
use in significant numbers on an
expendable basis.
The original project plan divided the
work into four phases:
Phase I: Systems Design and
Demonstration of Feasibility.
Phase II: Development of an
Operational Prototype.
Phase III: Testing and Refinement of
the Operational Prototype
System.
Phase IV: Addition of Elements
Necessary to Create a
Practical Research Tool.
Phase I was initiated in fall, 1983, and
ran through calendar year 1984. The
results were previously reported in the
Phase I report which gives the chain of
reasoning and the experimental data that
led to the operational prototype design
described here. Phase II spanned
calendar year 1985. Phase III began in
spring of 1986 and extended through
1987. The US EPA does not have
resources to support Phase IV.
Concept
Balloon systems obey Archimedes'
Principle: A body immersed in a fluid is
buoyed up by a force equal to the weight
of the fluid displaced. This implies that a
balloon system will be in equilibrium
when the weight of the air it displaces is
equal to the weight of the system.
Constant volume balloon (CVB)
systems have a unique characteristic.
The equilibrium condition is met only at
one well-defined altitude, and the CVB
seeks that altitude. If a CVB should I
itself above its equilibrium altitude, it
experience a net downward force due
gravity because the ambient air is li
dense at the higher altitude, and
volume of air displaced is fixed. Likewi
if a CVB should be below its equilibrii
altitude, it will experience a net upw.
force, since the buoyancy force excee
the gravitational force. Thus, CVBs te
to oscillate around their equilibrii
altitude, the oscillations driven
atmospheric turbulence. In atmosphe
flows that have zero average vertic
velocity, CVBs naturally follow tl
horizontal flow at their equilibria
altitude. However, in flows in which tl
vertical component is significant, a C\
will not adequately follow the overall flo\
The tracer balloon is a modified CV
It is designed to sense its deviation fro
the mean vertical flow, and to adjust i
buoyancy to keep its average vertic
motion relative to the air surrounding
near zero. Thus, the tracer follows bo
horizontal and vertical flows.
The buoyancy adjustment princip
used in the tracer was first put forward b
V.E. Lally of the National Center f<
Atmospheric Research almost 20 yeai
ago. He proposed a CVB with an inn|
bladder, or ballonet, to contain the lift ga
(helium). The remainder of the CVB wa
to be filled with air. A system of pump
and valves was included to allow air to b<
pumped in or released, respective!
increasing the mean density of thi
balloon and thereby decreasing it:
equilibrium altitude, or decreasing th<
mean density and thus increasing thf
equilibrium altitude.
Two basic approaches to the altituds
control problem were considered. Th<
first was to continuously measure th«
vertical velocity of the air relative to the
balloon, and to adjust the buoyancy sc
that on average, the relative velocity ol
the air is zero - that is, so that the
balloon and the air move together. The
second approach is to take advantage ol
the very nearly adiabatic nature o1
atmospheric flows. When flows are
adiabatic, the potential temperature (or
equivalent potential temperature in the
presence of liquid water) is constant
along each air parcel trajectory. In this
approach, the buoyancy is adjusted so
that the trajectory is isentropic. As long
as this condition is met, the balloon will
move along with the air surrounding it.
The approach to altitude control basei
on relative vertical air motion is very
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ect, but if it were to be used
Continuously for three days, the air
motion measurement would have to be
extraordinarily accurate. Under most
atmospheric conditions, the approach
based on potential temperature is quite
satisfactory, but in a layer of air in which
convective mixing is taking place,
potential temperature does not offer an
adequate guide to altitude control. Under
these conditions, the air surrounding the
balloon consists of turbulent flows
moving both up and down. The mixing
makes the potential temperature uniform
with altitude within the convective layer.
When convective mixing engulfs a
parcel of air, the main effect is to
disperse it and to spread it out in the
vertical, mixing it with air from all the
surrounding parcels. If a tracer balloon is
embedded in an air parcel that is
subjected to convective mixing as long
as the balloon remains in the mixed
layer, it lies within the confines of the
now greatly expanded "parcel." A
balloon following the expanding parcel
during convective mixing makes less
stringent demands on the buoyancy
control system than does one following a
arcel under stable conditions. Hence, a
.umber of different control strategies are
satisfactory under convective conditions.
Thus, an approach that makes use of
different control algorithms under
different meteorological conditions will
yield the best results. On the basis of the
sensor data, the on-board
microcomputer can be programmed to
determine which control algorithm will be
implemented at any given time.
The operational prototype currently
incorporates three control algorithms
selectable by radio command. The
control parameters for these algorithms
are relative vertical displacement,
potential temperature, and ambient
pressure. In a stable (non-convective)
atmosphere, in the absence of liquid
water, the potential temperature control
algorithm is most appropriate. In a stable
but saturated atmosphere, an algorithm
yet to be written using equivalent
potential temperature would be most
effective. In a convective atmosphere,
relative vertical displacement becomes
the control parameter of choice. Under
convective conditions, over reasonably
'lat terrain, even the constant pressure
jontrol algorithm may be satisfactory.
Operational Prototype
The operational prototype system
consists of the balloon envelope with its
pay load and a ground support station.
The balloon is a sphere of 2.9 m nominal
diameter (12.5 m volume) made of 3.0
mil bilaminated polyester with a 1.0 mil
full-volume polyethylene ballonet
inside. The balloons were made by
Raven Industries. The payloads consist
of a buoyancy adjustment subsystem,
sensors, a microcomputer, a telemetry
subsystem, a radio command
subsystem, a cutdown device, tracking
aids, and batteries.
An assembly drawing of the
operational prototype is given in Figure
1. The inner balloon is attached to the
outer balloon only at the helium fill fitting
located at the top. The bottom fitting, a
19 cm diameter nylon plate, was
modified to accept two fittings for air
lines, and electrical leads to
accommodate a pressure sensor
assembly inside the balloon. A larger
fitting, closed off in flight, was also
installed on the bottom plate to permit
rapid inflation and deflation.
The buoyancy adjustment subsystem
makes use of the same type of pumps
and valves used in the Phase I prototype.
The pumpdown speed - the rate at which
the equilibrium altitude can be lowered -
is determined both by the temperature
lapse rate and by the pressure head
against which the pumps must work, the
*superpressure." With 30 mb
superpressure, in a standard
atmosphere, the calculated pumpdown
speed with the three pumps used is
about 15 cm/s. The valves permit a rise
in equilibrium altitude about three times
faster.
The sensor subsystem consists of
three elements. The first is an aspirated
sensor assembly that measures ambient
pressure, temperature, and humidity. It is
a modified Atmospheric Instrumentation
Research Inc. prototype digital
radiosonde. The assembly outputs data
in ASCII format. The transmitter normally
in place has been deleted, and the
assembly has been housed in a
styrofoam package normally used for a
tethersonde, rather than a radiosonde.
The tethersonde package makes
provision for aspiration.
The second element is a second
modified digital AIR sensor assembly
mounted on the inside of the baseplate
to report pressure and temperature within
the balloon. No aspiration is provided for
this unit.
The third element is the vertical
anemometer. It makes use of a stock
22.9 cm (9 in) diameter expanded
styrofoam Gill propeller from R. M.
Young Inc., and a slightly modified
Spaulding Instruments Cl rotation sensor.
It has a starting speed under 2 cm/s, and
a measurement threshold of under 3
cm/s. This starting speed and low
velocity performance should allow
accurate relative vertical velocity
measurements averaged over minutes to
be made down to 1 cm/s or less.
The heart of the control system is an
Intel 8052AH BASIC microcomputer. For
Phase III, the memory was increased
from 4 K bytes of random access
memory (RAM) and 4 K bytes of
programmable read only memory
(PROM) to 16 K bytes each of RAM and
PROM. The control program is written in
BASIC and is entered into the
microcomputer from a terminal. To
provide reliable polling of the sensor
values, a Universal Syn-
chronous/Asynchronous Receive and
Transmit chip (USART) was added, along
with a machine language subroutine to
service the USART. A block diagram of
the payload system is shown in Figure 2.
Both telemetry and tracking are
handled through the Argos satellite-
based data collection and platform
location system. The Argos platform
transmitter terminal was made by
Telonics, of Mesa, AZ. It is uniquely
compatible with the flight control
microcomputer. It is controlled by ASCII
input commands.
The radio command receiver was
designed and built for application by
Sandia National Laboratories by Hock
Engineering of Boulder, Colorado. It
operates on 13.8035 MHz, a frequency to
which Sandia has access. It has a one
microvolt sensitivity. The command
receiver antenna is a quarter wavelength
wire which was attached to the skin of the
outer balloon, rather than left to trail
below.
Commands are electronically encoded
at the ground station transmitter, and
decoded at the receiver. In Phase II, the
encoder/decoder circuit pair were
commercially available components
designed for use in television remote
control systems. This system was found
to be highly vulnerable to electronic
noise. The command system was
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Figure 1. Assembly drawing of Phase III Tracer Balloon. A. Top fitting with cutdown device
and helium fill line. B. Vertical anemometer. C. Cutdown timer. D. Recovery beacon
(not flown on flight 2). E. External sensor assembly. F. Radar comer reflector.
G. Radio command receiver. H. Independent airsonde. I. Internal sensor assembly.
J. Bottom plate with valves and servo. K. Pump box. L Main electronics package.
M. Argos antenna. N. FAA transponder package (not flown in flight 1).
changed to be more noise resistant
through the use of dual tone
multifrequency coding. The same pair of
tones must be present on multiple
interrogations for the command to be
considered valid.
The commands currently available
are:
- activate cutdown
- reset cutdown timer
- turn on pumps (to lower altitude)
- open valve (to increase altitude)
- initiate control in pressure mode
- initiate control in potential
temperature mode
- initiate control in relative vertical
motion mode
- increment current value of control
parameter
- decrement current value of control
parameter
The encoder/decoder pair is capable of
incorporating many more commands with
minimal changes.
A cutdown device at the top of the
balloon releases the helium lift gas on
command. The rate of venting is such
that descent takes place at a safe
velocity. A cutdown timer automatically
actuates the cutdown device after a
preselected period. However, the timer
can be reset to zero by radio commanc
In normal operation, the timer rese
command is sent at frequent intervals. A
long as those commands are received <.
intervals not exceeding the preselectei
period, automatic cutdown is avoided. I1
on the other hand, radio communicatioi
with the tracer is lost for a perioi
exceeding that which has bee
preselected, the tracer is automatical!
removed from the sky. This arrangemer
avoids the possibility of the trace
becoming a derelict in the event tha
radio communication is lost.
For both test flights, a corner-typl
radar reflector was flown, and on thi
second flight, a FAA transponder witl
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System Block
Diagram
+5v
External
Sensor
Assembly
Internal
Sensor
Assembly
^,
^
-T»
USART
^
?
Computer
+5v
Wake-Up
^__
Voltage
Regulator
^
Lithium
Battery
+5v
Figure 2. Block diagram of Phase III Operational Prototype Pay load.
+Sv
encoding altimeter was flown. Thus far,
no night flights have been conducted,
hence a strobe light has not been
needed.
The batteries, lithium thionyl chloride
units in AA, C, and D cell sizes procured
from Altus Inc., are reported to have
excellent low temperature characteristics.
This property will be necessary to meet
the 5.5 km (500 mb) altitude design goal.
At this altitude, low temperatures will be
encountered. Preliminary tests with the
batteries have been conducted down to
-18 C.
The command and data reception
system used in Phase III consists of a
Handar Argos downlink receiver and
decoder, an IBM compatible PC (NEC
APCIII), a command encoder and
interface package, an ICOM model 745
transceiver with FM option and an
antenna coupler. A block diagram of the
system is shown in Figure 3. For the first
test flight, the system was mounted in ia
5-m Airstream trailer. For the second
flight, planned to be much longer, the
system was mounted in the Sandia de
Havilland Twin Otter instrumented
aircraft. The PC converts the Argos data
stream from hexadecimal to decimal
form, formats it, provides a hard copy
listing of the results, and stores the
results on the NEC internal hard disk.
Inflation of the Tracer Balloon in the
field without shelter would be very
difficult. For Phase III, a conventional
hangar at a conveniently located airport
was used.
Results and Discussion
The Phase III test flights were
launched from Sandia Air Park, a small
airport about 40 km east of Albuquerque
near the community of Edgewood. This
site is east of the Sandia and Manzano
Mountains, so flights made under the
influence of the usual westerly winds
would not immediately encounter rough
terrain.
The first flight was planned for an
altitude of about 300 m. To aid recovery
and tracking, a Telonics radio beacon
designed for animal tracking was flown.
Liftoff of flight 1, shown in Figure 4,
occurred at 10:49 a.m. on August 13,
1987. Winds at the surface at launch time
were estimated to be gusting to 15 kts.
For this flight, the Argos antenna on the
balloon was a high gain device designed
by NCAR for use on high altitude
balloons. The radiation pattern of this
antenna is primarily vertical, thus making
reception at the ground from a system at
low altitude to the ground difficult. With
the high winds encountered in this first
flight, the Tracer Balloon was carried out
of range of the data reception within a
quarter of an hour. Data from the AIR
sonde attached to the skin of the balloon
was received for about a half hour, until a
parked aircraft came between the ground
antenna and the Tracer Balloon. The AIR
signal was reacquired just before
touchdown, but by that time the Tracer
was no longer in sight. The Tracer
Balloon appears to have responded to
commands throughout the flight. It was
decided, given the loss of reception of
the Argos data at the ground station, to
allow the automatic cutdown timer to
terminate the flight. Touchdown occurred
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Ground
Station
Components
H.F.
Antenna
ARGOS
Antenna
(401.65 MHz)
\ Keyboard]
Figure 3. Block diagram ol Phase III command and data reception system.
14 km of the launch site, at about 11:59
a.m.
The second flight was planned for an
altitude of about 1000 m. The addition of
the Terra FAA transponder added 1.8 kg
to the balloon payload. To provide
adequate lift, a zero pressure balloon
was attached to the top of the adjustable
buoyancy balloon. In this way, ignoring
thermal heating of the balloon by solar
radiation, the weight of the transponder is
balanced by the lift of the zero pressure
balloon independent of altitude.
Launch of the second test flight
occurred at 1:29 p.m. of January 13,
1988. About 12 minutes into the flight,
the balloon had risen to about 110 m
above ground and was about 1.5 km
from the launch site. At that level, the
Tracer encountered a violent wind shear.
Below this level, the winds had been light
and from the southeast. Above 110 m
altitude, winds were much stronger and
directly out of the west. The shear was
so violent that the rigging holding the
main electronics package and the
transponder to the main balloon gave
way. It is speculated that the coupled
oscillations induced by the shear in the
complicated tandem balloon system may
have been responsible for whiplash of
the payload packages resulting in high
g-forces.
The tandem balloon system, released
from much of its burden, began to rise
rapidly. With the loss of the electronics
payload, automated control, remote
command control, and the Argos data
link were lost. The AIR sonde velcroed to
the balloon skin remained and continued
to send data. The main and auxiliary
balloons remained together and rose to a
maximum altitude of about 5200 m
(17,100 ft MSL), and then came slowly
back down. The chase aircraft caught up
with the balloons as they passed through
3800 m on the way down. From the
aircraft, there was no visual evidence of
catastrophic failure of either balloon
envelope. Rather it appears that the thin
membrane which is part of the cutdown
device on the main balloon served as a
pressure relief device and blew out when
the superpressure exceeded the strength
of the membrane or the membrane
holder. It is known from the cutdown
timer setting that the cutdown device
would not have fired before the balloon
began descending. The aircraft followed
the tandem balloon system until it
touched down about 16 km west of the
village of Anton Chico, NM at about 2:50
p.m., about 83 km from the launch site.
Recommendations and
Conclusions
Problems with damage to the inner
ballonet on installation in the outer
balloon during the manufacturing process
need to be overcome. Leaks at the top
and bottom fixtures need to be
eliminated by improved design. Failure of
the circular top seam joining the gore
structure to the top mylar piece must be
eliminated by proper reinforcement at th<
factory. These problems must bi
eliminated if the technology is to set
routine use.
Clearly the rigging of the payloa<
needs to be improved to assure that it i:
not possible to lose the payload ii
turbulence or wind shear. It is noted tha
the packages velcroed to the skin of th<
balloon appear to have survived withou
difficulty. Attaching all of the packages ii
this way may be a satisfactory solution.
The control software still does no
contain provision for either an "effectivi
potential temperature" control algorithm
or provision for self-selection of th<
control algorithm. Both should b<
implemented.
The command and data receptioi
system currently makes use of a Handa
Argos receiver and decoder. It i
obsolete, and in a cold environment
does not function properly. It should b
replaced. For long Tracer Balloon flight;
use of a chase aircraft will prove to b
very convenient - provided comman
and data reception system are availabl
both on the ground and in the aircraf
This would require a second comman
and data reception system.
At the end of the Phase I and Phas
II reports, the authors concluded that a
adjustable buoyancy tracer balloo
meeting the design goals is bot
technically and economically feasibk
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Figure 4. Tracer Balloon shortly after liftoff of flight 1. which occurred at 10:49 a.m. on
August 13, 1987.
Phase III continued to confirm that
conclusion. It remains to be
demonstrated, however, that those
design goals have in fact been fully met.
Nevertheless, the Tracer Balloon system
is already a useful atmospheric research
tool.
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8. D. Zak is with Sand/a National Laboratories, Albuquerque, NM 87185 and A.
W. Uchfield is with Spectra Research Institute, Albuquerque, NM 87109.
J. S. Irwln and R. G. Lamb are the EPA Project Officers (see below).
The complete report, entitled "Development of an Adjustable Buoyancy Balloon
Tracer of Atmospheric Motion: Phase III. Refinement of the Operational
Prototype System," (Order No. PB 88-190 764/AS; Cost: $32.95, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
AUG;l'88
rn q
,. U .-J
Official Business
Penalty for Private Use $300
EPA/600/S3-88/015
0000329 PS
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