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3
Observing Systems
The weather sensitivities of the space program demand mea-
surements of parameters quite different from those made for use in
providing the public with weather forecasts. The types and sizes
of precipitation particles in clouds and the potential for triggered
lightning are just two examples. Because of the special requirements
of the space program, certain deficiencies exist in the observational
program at KSC and other sites that can be remedied by a combi-
nation of upgrading existing systems, acquiring and deploying new
equipment now available, and conducting applied research to develop
needed equipment not yet available anywhere in the world. These
activities range from adding displays and calibrating instruments,
which could be accomplished in a few days, to applied research that
could take a few years. Improvements should be planned and coor-
dinated by the Weather Support Office (WSO).
Most of the critical weather elements discussed in Chapter 1
cannot currently be observed with the high degree of accuracy re-
quired in an endeavor as weather-sensitive as the space program,
where small errors can produce catastrophic results. Although most
public-service forecasters would be pleased to be correct 90 percent
of the time in yes no forecasts of precipitation, an accuracy that
low for any of the weather elements critical for space flight could be
devastating. The inescapable conclusion is that accuracies of about
99 percent or greater are needed when critical failures would result.
27
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This requirement almost certainly dictates that Sections concerning
weather-sensitive operations (1) will always be made as late as possi-
ble, (2) will be based largely upon observations at decision time, and
(3) should err in favor of postponing the weather-sensitive activity if
critical weather is even a slight possibility. Thus, aside from planning
efforts that require forecasts for days or longer, the forms of weather
information most important for space operations are diagnoses of ex-
isting conditions and very-short-term weather forecasts for periods
of several hours or less.
As long as launches are infrequent and delays are tolerable, there
is likely to be little pressure on the system. However, as launches
become more frequent, weather-related delays will be less tolerable,
and therefore improved capabilities for detection and forecasting of
adverse weather are needed. How unfailingly can state-of-the-science
instruments adequately detect critical weather elements? How well
can state-of-the-science methods be used to forecast critical weather
elements for 2-hour intervals?
This chapter gives an overview of (1) some of the existing mea-
surement systems used at KSC (and, to a limited extent, at other
sites), (2) other systems available for deployment, and (3) remaining
needs for development of instrumentation to observe a few important
meteorological parameters.
UPP1:R-AIR SOUNDINGS
High-resolution vertical profiles of wind speed and direction are
needed to assess wind loads on the launch vehicle during launch
and landing. The jimsphere balloon, tracked by radar, provides
the greatest vertical resolution in measuring winds aloft. Data are
normally obtained at 100 foot (atom) intervals. Jimspheres provide
the data used in assessing the wine! loads prior to launches at KSC
and Vandenberg.
Near the jet stream there can be large wind variations in less
than 2 hours that could male prelaunch balloon-based soundings
unrepresentative of launch conditions. Balloon-based wind profiles
require about an hour to measure winds to 55,000-foot (17 km)
altitudes, so it is impossible to obtain soundings at less than 1-hour
intervals unless multiple tracking devices are available and several
balloons are airborne at the same time.
Doppler wind profilers, which have been under development for a
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decade, are in operation in a number of places worldwide. Although
their vertical resolution is somewhat poorer than that of the jim-
sphere system, wind profilers can provide data at intervals as short
as 30 seconds, if desired. There are plans to install a Doppler wind
profiler at KSC before the end of 1988.
The wind profilers should be installed at and surrounding KSC
in order to monitor important changes in the wind. Wind and wind
shear data, as well as spectrum width of the profiler winds (which is
related in part to turbulence within the beam), should be collected.
Once a suitable profiler data base ~ attained, the method of as-
sessing launch wind load hazards to the shuttle should be examined.
It should be determined if a network of wind profilers at and sur-
rounding KSC could be used to obtain very-short-term forecasts of
wind profiles at launch tune through advection of wind field patterns
across the network. A numerical mode! might be helpful in making
these forecasts.
The type of wind data really needed during a launch is a profile
along the launch trajectory. Neither balloons, which drift with the
wind, nor profilers can provide this type of sounding. Aircraft are
better suited to provide this type of information, but the present
prelaunch aircraft are not instrumented to make accurate wind mea-
surements. The program of prelaunch reconnaissance flights using
T-38 and Shuttle Training Aircraft should be upgraded either by
adding instrumentation to these aircraft or by using other available
instrumented aircraft. Quantitative measurements should be made,
over and upwind of KSC, of cloud electric fields, the types and
sizes of precipitation, electric fields and Maxwell currents, winds,
wind shears, and turbulence. A computerized data collection system
should be used to facilitate the real-time collection and archiving
of these data, and also to transmit the data to KSC forecasters for
timely use. MSFC should explore the possibility of using these data
as part of the DISC loads assessment program.
Thermodynamic soundings (temperature and relative humidity)
are needed to obtain atmospheric density profiles during launches.
These are obtained by balloon-based instruments, particularly the
ground meteorological detector (GMD)-tracked radiosondes, and by
rocketsondes. These systems should be assessed against the state
of-the-science technology, such as Loran-based balloon tracking sys-
tems. The latter have proven far superior to GMD systems for
obtaining accurate wind speed profiles during field research experi-
ments, especially during situations of strong winds aloft and in terms
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of vertical resolution. Furthermore, the National Center for Atmo-
spheric Research (NCAR) Cros~cha~n Loran Atmospheric Sounding
System (CLASS) has been designed and demonstrated to operate
nearly automatically, and would potentially provide better data with
less manpower and cost than the present GMD system.
Remote soundings of temperature and humidity, obtained via
satellite-based radiometric profiling, currently have vertical resolu-
tion that ~ too coarse for use in the space program. WSO should
monitor the progress of research on these systems and be prepared
to put them into use in the space program, should their resolution
improve.
To obtain better htformation about spatial and temporal
variation of the wind near ESC, NASA shoed establish
a network of Doppler wind profilers and a program for en-
hanced aircraft observations mmg avaBable NASA and U.S.
Air Force aircraft.
BOUNDARY LAYER AND SURFACE WEATHER
Near-surface winds are important for landings, launches, and
ground operations, and can be measured accurately and at very fre-
quent intervals (1 minute or less) using automated weather stations.
A system of this type, called WINDS (Weather Information Network
Display System), is used at both KSC and Vandenberg, with sen-
sors on towers from 54 to 500 feet at KSC and 12 to 300 feet at
Vandenberg. Winds from these networks are available at A, 15-, or
3~rntnute intervals. Shorter intervals may be desired in the critical
minutes before launch, when passage of a gust front (outflow from a
distant thunderstorm) or the sea breeze front (moving in from sea)
could cause dramatic changes of wind direction and speed.
The existing automated surface mesonetwork (28 stations) is
a critical element in the observational program at KSC. It should
be expanded to the west to cover the western portions of the KSC
activity domain (and procurement of 20 additional stations is in
progress), and to the east to include measurements over water, via
buoys or platforms for routine operations and/or via ships during
launch situations. The instrumentation should be expanded to in-
clude visual range transm~ssometers at the launch pads and the Shut-
tle landing field airstrip. The individual sites should be adjusted, if
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necessary, to ensure that the observations are taken at uniform al-
titudes, with proper exposure and sheltering, and with uniform and
well-ma~nta~ned instrumentation.
A Doppler sodar (sonic detection and ranging) can be used to
monitor the low-level (up to about 1 km) wind profile at 5-minute
interval except during precipitation. This instrument has better ver-
tical resolution than the wind profiler, 80 Doppler sodars would be of
value in augmenting the tower wind network. Such data would prove
invaluable for dispersion forecasting and in providing information
regarding other surface operations. A Doppler Acoustic Sounding
System (DASS) is currently operated at Vandenberg.
The horizontal distribution of low-level winds provides important
information for weather forecasting. Small-scale fronts and wind
shift lines can escape detection if stations in a mesonetwork are more
than several kilometers apart. Scanning Doppler weather raciars and
Doppler lidars can supply the type of spatial coverage needed to
locate such wind shift lines. A NEXRAD Doppler racier ~ expected
to be installed at Melbourne, Florida, about 25 miles south of KSC,
in 1990.
Because a single Doppler radar can detect motion only along a
radial, a network of at least two Doppler radars should be deployed
at KSC ~ order to resolve tote] horizontal velocities. Unfortunately,
the NEXRAD radar to be deployed at Melbourne within the next
several years will not scan in a manner conducive to multiple Doppler
radar studies in consort with another radar. NASA should acquire at
least two dedicated Doppler radars, which would enable calculation
of detailed patterns of winds in clouds and in the boundary layer. To
make the wind calculations in real time would require the develop
ment of new dual-Doppler data processing and display software. In
addition to horizontal mappings of velocity, cros~sections along the
space vehicle flight path could also be constructed.
1~ obtain enhanced information about low-le~re} wmds and
other weather elements, NASA should emend the areal cov-
erage of the surface mesonetwork and Include data platforms
over the ocean. At least two dedicated Doppler radars shown
be installed in locations that optimize coverage over KSC
to improve forecasts 1lemg higher resolution boundary layer
data and to better relate the wmd fields and refiectivity
withm clouds to the microphysical and electrical develop
meet. NASA Should consider deploying Doppler sodars for
mowtoring the boundary layer.
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32
PRECIPITATION
Showery precipitation often falls over areas of only a few square
kilometers, and rain gauge networks are rarely dense enough to
resolve this detail. Conventional (non-Doppler, incoherent) weather
radar can be used to obtain high-resolution mappings of areas with
precipitation. Forecasters use the horizontal and vertical shapes
of the radar "echoes and the intensity of the echoes to identify
convective and stratiform precipitation. Satellite imagery can also
be used to help identify convective clouds. However, neither radar nor
satellites can unambiguously distinguish thunderstorms from other
types of convective precipitation.
State-of-the-science weather radars provide digital data that can
be processed by computerized software packages to derive additional
useful products such as vertically integrated liquid water contents,
cross sections of reflectivity at any desired angle, and animated im-
agery. The 30~year-old FPS-77 radar at Vandenberg is not digitized
and provides the forecaster only with snapshot views at fixed az-
imuth or elevation angle. A radar should be deployed at Edwards
AFB, and digital radars should be considered for both Vandenberg
and Edwards.
The thermal tiles on the Space Shuttle are eroded by precipita-
tion drops. However, there is a need for more detailed information
relating drop size and concentration to the extent of the tile damage.
Unfortunately, drop sizes cannot be measured using conventional
radar. Surface-based disdrometers are typically used to measure
raindrops reaching the ground, and an aircraft-mounted Knollenberg
probe can be used to sample sizes of precipitation aloft. These types
of instrumentation are not currently used in space operations, but
should be.
A possible tool of the future is the multiparameter radar, which
transmits at two wavelengths and with two polarities. Multiparam-
eter radars can distinguish between snowflakes, raindrops, and hail,
and between large drops and small drops. However, certain ambigui-
ties exist, such as melting snowflakes. Additional research should be
done to enable this tool to be utilized operationally.
To obtain data on cloud and precipitation types and sizes, air-
borne tIrop-size measuring instrumentation should be flown
prior to Space Shuttle launches, and a mo~tiparameter radar
should be acquired.
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33
LIGHTNING
During the summer at KSC there is an average of about six
lightning strikes to ground per square mile each month. Until the
last decade, it was extremely difficult to detect and locate lightning
strikes on a real-tune basis. Cloud-to-ground lightning strikes can
now be successfully detected by using either magnetic direction-
finding (Lightning Location and Protection (ALP)), omnidirectional
broad-band time-of-arrival (TOA) antennae (Lightning Position and
Tracking System (LPATS)), or by careful interpretation of electric
field mill network data. (Other methods also exist, such as lightning-
detection ra`lar and lightning interferometers.) Lightning strikes
are typically located with position accuracies of 2 km or better by
triangulation. An LLP system is in operation at KSC; it should be
improved by periodically checking the site correction factors and the
antenna alignments.
Two larger lightning detection networks cover the KSC area: a
network of LLP direction finders operated by the State University
of New York at Albany and the Florida LPATS network of broad-
band TOA receivers. Displays of these data should be added to the
KSC weather office. Data from the SUNY Albany system showed
the movement of an area of considerable cloud-to-ground lightning
activity toward KSC from the west prior to the AtIa+Centaur 67
accident, as shown in Figure 4. Had these data been available in
the KSC weather office, it is likely that the launch would have been
postponed, averting the accident.
At KSC, at present, in-cloud and cloud-to-cloud lightning dim
charges are difficult to detect. These occurrences can be inferred
from data provided by the Launch Pad Lightning Warning System
(LPEWS), a Gestation network of field mills that is clesigned to de-
tect electrified clouds. Because the LPEWS is the only network of
its kind in the world, few meteorologists have been exposed to these
data for use in real-time weather analysis and forecasting. Persons
who would typically provide forecaster training are not usually well
versed in this tool, and those familiar with field malt network inter-
pretation are usually more adept at using it in a research rather than
an operational environment.
The LPL.WS is currently being upgraded. The sensors should
be improved, and the sites should be carefully evaluated to identify
any local obstructions or sources of contamination, and obstructions
should be removed or sites relocated, if necessary. The network
should be expanded to the west and to the east, including over-water
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34
..- -
I_ \~j.~;~. U
.- ~.~' ~ -- eF ~
~, , ~ _
:~ _ ~ ___
~_~-
r ~`LAUNCH
, SITE
_
_
=
e
_
R
~_
TIMES UTC
.
·1823-1923
·1923-2023
·20 23-21 23
FIGURE 4 State University of New York (SUNY) at Albany display of LLP-
detected cloud-to-ground lightning prior to the Atlas-Centaur 67 launch. In the
3 hours prior to launch, lightning activity progressed steadily across Florida
toward KSC. (Courtesy of R. Orville, State University of New York at Albany.)
sites. The equipment should be carefully calibrated and certified for
operational use, and the observations included in the list of weather
criteria for launch (and landing).
In-cloud and cloud-to-cloud lightning can also be detected by
using networks of (1) HF or VHF time-of-arrival receivers or (2) HF
or VHF lightning interferometers. A system (LDAR) of the former
type was previously operated at KSC but abandoned. A new system
of this type should be built.
The National Aeronautics and Space Administration should
make improvements to the existing LIP and [PEWS systems
and obtain displays of other lightning detection networks in
the area, ~ order to improve detection of lightning and elec-
tric fields. A new system should be blight to detect lightning
in and between clouds aloft.
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35
DCLOU ELECT lIC FI1:IDS
Clouds, such as thunderstorm anvils, stratiform thunderstorm
anvils, stratiform clouds, and shallow convective clouds, often do
not produce lightning but do contain high electric fields. The threat
of triggered lightning from these clouds may be the most difficult
weather hazard to detect and forecast. Surface electric fields do not
always reveal electric fields aloft or charge centers in the upper por-
tions of clouds, because of the presence of intervening (or screening)
charged layers. Airborne electric field mild systems, such as those
formerly used on the NASA F10~B research aircraft, should be used
to accurately characterize the electrical environment aloft.
Much of the data collection and research on the subject of trig-
gered lightning has been sponsored by KSC, so that the center's
triggered lightning research is state-of-the-science within the atmo-
spheric electricity community. Additional efforts are needed to add
companion meteorological data (such as radar data, surface mesonet-
work and tower data, satellite data, and sounding data) to the trig-
gered lightning data base for possible forecasting applications and to
provide training to operational forecasters concerning the use of field
malt network data. Airborne measurements using field mats repro
sent an import ant contribution to better defining the potential for
induced lightning.
The new launch criteria, designed to avoid any possibility of
triggered lightning, may have become overly conservative with re-
gard to cloud electric fields. To addre" this issue, one or more
instrumented aircraft should be flown on frequent occasions in order
to develop a cI~matolog~cal data base reg=ding electric fields and
Maxwell currents in ~dead" or detached anvils and anvils from dim
t ant thunderstorms. Data should also be collected in other types of
cloud near the freezing level.
Triggered lightning studies shown be continued, with addi-
tional efforts to collect companion meteorological data sets.
A'rbo~e electric field measurements shown be collected to
enhance studies of the threat of triggered lightumg.
OTHER WEATlIER ELEMENTS
Dangerous icing conditions will result if a vehicle encounters
supercooled (i.e., liquid at subfreezing temperatures) cloud and pre-
cipitation drops. Owing to the poor spatial coverage of rawinsonde
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data and since conventional weather radar cannot distinguish be-
tween precipitation sizes or types, regions conducive to aircraft icing
are very difficult to detect. Pilot reports are the main source of infor-
mation. Multipararneter radar, combined with temperature profiles,
might prove useful for detecting and avoiding freezing rain. Cloud
radars (wavelength of approximately 3 mm), which detect cloud-
sized particles, may prove useful in supercooled cloud detection, if
used with sounding data.
Clear-a~r turbulence, which arises within layers of large vertical
wind shear, ~ very hard to detect. It is most commonly detected and
reported by pilots. Some information regarding shears and hence
the possibility of turbulence can be derived from the spectrum width
of Doppler radar data, both from scanning Doppler weather radar
and from Doppler radar wind profilers. Much work remains to be
done, however, in calibrating the spectrum width values against the
incidence of turbulence. Satellite imagery can also often be used to
alert forecasters to areas where turbulence is likely.
Trained weather observers can also provide valuable data to the
weather forecaster. An observer has the unique ability to assimilate
audible and visual data in a manner that is better than most instru-
ments. To obtain quality information, the observers must be trained
to identify the specific conditions that may be conducive to weather
hazards such as triggered lightning. At KSC, the weather office has
no windows, and forecasters cannot see outside without climbing to
the roof. It would be desirable to move the forecasting operations to
a room with a window or to make a window in the room currently
used, so that observers could more easily monitor rapidly changing
atmospheric conditions.
Trained and reliable observers and adequate facilities are needed
at all sites overseas and in the United States. The pane! does not feel
comfortable with past arrangements for obtaining weather observa-
tions at overseas landing sites.
The National Aeronautics and Space Administration should
ascertain that launch and landing sites are provided with
skilled observers and necessary measurement systems. NASA
should monitor the achievements in observation technology
and deploy usefid new instrumentation expediently.
Representative terms from entire chapter:
triggered lightning
