WWV Moves to Colorado - Part II
February 1967 QST Article
is the second of a two-part series on the move of the WWV transmitter
stations operated by the National Bureau of Standards (now called
National Institute of Standards and Technology) from Greenbelt,
Maryland, to Boulder, Colorado.
WWV Part I appeared in the January 1967 edition of the ARRL's
QST magazine. WWV began transmitting time / frequency standards
in 1920 in order to provide a means for remote stations and laboratories
to calibrate local standards that would prevent transmitting stations
from interfering with each other. Although most people don't realize
it, the 60 kHz signal that their 'atomic' clocks and watches
use to self-adjust time emanates from the WWVB antenna in Boulder.
The first installment of the article discusses the history and rationale
for relocating the WWV facility to a new location. This second part
gets into the technical aspects of the WWV facility's equipment
and operation. As usual, I am amazed at the pioneers who conceived
of, designed, and implemented these kinds of operations.
February 1967 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present (visit ARRL
for info). All copyrights hereby acknowledged.
Note: I wrote a short story on
WWVB a couple years ago.
WWV Moves to Colorado
In Two Parts: Part II
By Yardley Beers, W0EXS
earliest function of WWV was to transmit standard carrier frequencies
to provide frequency calibrations so that radio stations could stay
on their assigned frequencies and avoid mutual interference, and
to allow persons having receiving sets and wavemeters or frequency
meters to calibrate them. Indeed, it is this feature of the broadcasts
which is of chief interest to amateurs today. However, in the course
of history the usefulness has been greatly increased by superimposing
time markers and other information by a suitable program of modulation.
In addition, mainly because of the needs of stations used for tracking
of rockets and space vehicles, the present accuracy is far in excess
of that required for the original purpose. However, for the moment,
we shall confine our remarks to this original function.
clearly, if the objective of avoiding interference between stations
on adjacent channels is to be accomplished, all frequency measurements
must be coordinated: that is, they must be referred to a single
standard. Similar reasoning holds for countless other physical quantities:
length, force, speed, voltage, current, resistance, power, to name
a few. However, most of these are not independent. They may be related
by definition. For example, if one measures the time necessary for
an object to travel some previously-measured distance, he can determine
the speed. Or they may be related by physical laws. For example,
if a known current flows through a wire of known resistance, the
voltage drop between its ends, as measured by a voltmeter, must
agree with that computed by Ohm's Law.
Thus, to digress for a moment, we are led to the concept that all
the physical measurements within the U.S.A. form the National Measurement
System. This System is involved in essentially all activities of
commercial and private life. It makes it possible to assure a housewife
that when she pays for a pound of meat in a Denver supermarket she
will receive the same amount of meat as when she shopped at her
former market in Chicago. It makes it possible for the piston of
an automobile motor made in Detroit to give proper performance when
used in a cylinder block made in New Jersey. This System is something
far greater than the National Bureau of Standards, but the Congress
has given the Bureau the responsibility of providing "the basis
for accurate and consistent measurements": that is, for providing
standards and for leading the coordination of measurements within
Sadami Katahara, KH6DK, engineer-in-charge, makes adjustment
to frequency control equipment at WWVH.
Richard F. Carle K0LYM, engineer-in-charge of WWVB-WWVL, with
some of the frequency control equipment of that station.
Fig. 1. Accuracy of WWV broadcasts as a function of time. Solid
curve gives accuracy of the transmitted signal. Dashed curve
gives accuracy of received signal at about 1,000 miles from
transmitter. Degradation of accuracy is due to propagation effects.
See text for information on present accuracy.
However, the coordination is not solely confined
to measurements within the U.S.A. Frequency measurements must be
consistent with those outside if international QRM is to be avoided,
and manufactured goods on the international market must have specifications
given in units which are internationally significant. Therefore,
NBS is further given the responsibility of making international
comparisons. As part of its coordinating role, NBS must participate
in the standardizing of the units and definitions of quantities.
As the result of the recommendations of international committees
to which NBS is a party, NBS has adopted for its own use the hertz
as the unit of frequency, and it is encouraging others to do the
same. For this reason, this unit is used in this article.
In the hierarchy of measurements, "frequency" and the very closely-associated
quantity "time" collectively play a very important and unique role.
It has been stated above that the measurements of many quantities
are interrelated. In fact, the interrelations are so numerous that
it can be shown that the system of measurements of physical quantities
is based upon the units of just four quantities; frequency-time
is one of these, the others being length, mass, and temperature.
Also, it is the only unit for which the user can obtain instantaneously
a virtually direct calibration against the NBS Standard in his laboratory,
factory, or home. For this latter reason, there is an effort to
convert measurements of other quantities into measurements of frequency
by the use of suitable transducers.
Considerations of Time and Frequency
If the reader
is to appreciate fully the significance of the WWV broadcasts, it
is necessary to review some fundamental concepts. The measurements
of both time interval and frequency are based upon some physical
phenomenon which ideally is perfectly repetitive - or which, if
not exactly repetitive, is accurately predictable, such as the oscillations
of a piano string, the motion of a pendulum, or the electrical oscillations
of a resonant circuit composed of an inductor and capacitor. Until
recently, the most accurately-predictable repetitive phenomenon
available was the revolution of the moon around the earth (although
the results are generally expressed in terms of the time-equivalent
motions of the earth about the sun). Until recently all measurements
of time and frequency have been referred to this. However, it is
now generally believed that the electromagnetic radiation emitted
by atoms and molecules is much more uniform, and that there is no
physical reason to suppose that there should be any variation provided
the atoms are either isolated or maintained under constant environmental
conditions. Therefore, the best present standards of time and frequency
are based upon these atomic radiations. Measurements of the motions
of the earth and moon referred to them reveal nonuniformities in
these motions which are quite trivial from the human point of view
but which, scientifically speaking, are very significant.
A standard frequency is determined by the number of cycles of
the reference phenomenon per second of time. Conversely, if one
counts the number of cycles of standard frequency which occur between
two events, he can ascertain the time interval between those events.
Thus, a clock consists of (a) a physical configuration which gives
rise to a repetitive phenomenon and (b) a device which counts oscillations.
When one is counting the intervals between large numbers of events,
it is convenient to refer measurements to one particular event,
which is said to define the "epoch" of a time scale. For example,
when we speak of the year 1966 A.D., we are speaking of a time scale
for which the epoch is defined by the birth of Christ, and we are
referring to some event occurring 1966 years later, approximately.
The unit of time used by scientists is the second, and at present
this has two different definitions. One of these, called the "Ephemeris"
second, is based upon astronomical measurements, and we shall not
give the details here. The other, the "atomic" second, is the time
interval required for exactly, 9,192,631,770 cycles of the radiation
absorbed or emitted by a certain transition of isolated cesium atoms.
This last statement is equivalent to saying that, by definition,
the frequency of this radiation is exactly 9,192,631,770 hertz.
These two definitions of the second are consistent; that is, if
one were to refer any given time-interval measurement either to
appropriate astronomical observations or to the cesium atom, he
would obtain essentially the same result for the first several digits,
but he would find the measurements relative to the cesium atom to
be more precise: that is, more of the digits in his answer would
be meaningful. Furthermore, if one has the proper apparatus, measurements
relative to the cesium atom can be carried out much more conveniently
than the astronomical ones. Mainly for the first of these two reasons,
atomic measurements are preferred for accurate scientific work.
Frequency and time are the primary business of WWV, and the
physical facilities described in Part I of this article exist
solely for the dissemination of highly accurate information
about these two quantities. The article concludes with a description
of the basic standards used for this purpose, how they are used
to control the transmitters, a brief history of WWV and a description
of the NBS organizational setup that is responsible.
At the present, two types of time scales have been established for
people who have need for accurate time measurements. One of these
is Atomic Time, which does progress uniformly, in principle. The
other is Universal Time, which progresses in synchronism with the
slightly-irregular rotation of the earth; this is required for earth
navigation. To generate Universal Time from Atomic Time, it is necessary
to compensate for the irregularities of rotation. The most widely-used
type of compensation involves a combination of (a) offsetting the
frequency of the oscillator in the clock by an amount determined
by the International Time Bureau in Paris and (b) by making occasional
step adjustments of 0.1 second, as determined by the International
Time Bureau in consultation with astronomical observatories all
over the world. At present, the frequency offset is three parts
in a hundred million lower than specified by the definition of the
second, an amount much too small to be noticeable by radio amateurs
and many others, but large enough to be important to those who track
satellites. This offset is held constant within any calendar year,
but frequently it has been necessary to change it from year to year.
Therefore, many people feel it would be better to eliminate offsets
completely and use only step adjustments, even though there would
be a few more of them. This subject received considerable attention
at the 1966 meeting of the CCIR (International Consultative Committee
on Radio) in Oslo, and as a result of agreements made there, the
use of offsets, which has been mandatory in standard-frequency transmissions
on certain frequencies, is now optional. It is likely that in the
near future many standard frequency transmissions will eliminate
At the present time, however, the frequencies of WWV,
WWVH, and WWVL are offset, and their time signals are on the so-called
NBS-UA Time Scale, which is generated by an atomic standard but
which is compensated by the offset and by step adjustments to agree
with Universal Time within about 0.1 sec. On the other hand, 60
kHz is not one of the frequencies covered by this international
agreement, and at the present time the frequency of WWVB is not
offset; the time is broadcast in accordance with the so-called Stepped
Atomic Time Scale (SAT), which uses 0.2 sec. step adjustments only
to keep within approximately 0.1 sec. of Universal Time. The offset
and step adjustments of the NBS-UA Scale are determined by the International
Time Bureau on the basis of data supplied from many sources. Step
adjustments of the SAT Scale are determined by NBS on the basis
of data supplied by the U.S. Naval Observatory. When a step adjustment
is made on either scale, it is made at the beginning of a month
and announced in advance in the Federal Register and in publications
of the IEEE.
While WWV, WWVH, and WWVL broadcast time on
one scale and WWVB on another, Universal Time on either scale can
be obtained from any broadcast by means of corrections partly coded
in the broadcasts. The details of how this can be done, and much
other information concerning the broadcasts, can be obtained from
History and Accuracy of NBS
The first broadcasting conducted by NBS,
in 1920, was on an experimental basis in order to gain technical
competence. For a brief time entertainment and market reports were
transmitted for the Department of Agriculture. Although speech and
music were transmitted, code was used for the reports. After a short
time, this work was discontinued. It should be noted, however, that
these broadcasts preceded the much more publicized pioneering broadcasts
Regular standard frequency broadcasts
from WWV started on March 6, 1923, with the station originally located
upon the grounds of NBS in Washington. (Some previous experimental
tests had shown that wavemeters owned by some of the listeners were
off by as much as seven percent!) Originally transmissions took
place only a few hours a day, and spot frequencies were transmitted
in accordance with a previously announced schedule. These frequencies
ranged from below the a.m. broadcast band to considerably above.
After a brief interlude in College Park, Maryland, the station
was moved in 1932 to a site near the now-discontinued station in
Greenbelt, Maryland. In 1931 essentially continuous operation on
5 MHz was initiated and, while oscillators using quartz crystals
had been used for reference for some time previously, at that time
the frequency of the station became directly crystal controlled.
Operation on various spot frequencies continued as before for a
time, but it tapered off while continuous operation on 2.5 MHz and
on integral multiples of 5 MHz were gradually added to the service.
On November 6, 1940, the station was demolished by fire. By ingenuity
and hard work, a new station was improvised and put on the air within
a few days. On August 1, 1943, the station went on the air with
improved "permanent" facilities in Greenbelt. In 1948, similar broadcasts
were initiated from WWVH in Maui, Hawaii on some of the same frequencies
(at present 2.5, 5, 10, and 15 MHz.)
The accuracy of the
carrier frequencies of these broadcasts, as to be expected, increased
with time by many orders of magnitude, as indicated by the solid
curve of Fig. 1, which gives the accuracy of the ground-wave signal.
This improvement was due to the innovation of improved reference
standards and control methods, as noted on the figure. At present,
the accuracy is of the order of a few parts in a million million
(1012), and the control system is so good that this closely
approaches the accuracy of the NBS Atomic Standard. It is, of course,
far in excess of that needed by radio amateurs and other services
for keeping their transmitters on assigned frequencies. If an amateur
can measure a 50-MHz signal with an accuracy to 50Hz, he would probably
consider that his accuracy is far greater than he needs. Yet this
would be only one part in a million (106). Needs for
other transmitting services are hardly any greater; only the tracking
of satellites and pure science require this extreme accuracy.
It is to be noted that a spectacular increase in accuracy resulted
from the introduction of the use of a cesium atomic standard. The
cesium atoms give a resonance which corresponds to a Q of about
100 to 1000 million, which exceeds that obtainable from quartz crystals
and is far in excess of that obtainable from inductors and capacitors.
Also, the cesium standard is far less vulnerable to environmental
effects such as changes in temperature. At present, NBS and many
other laboratories are continually improving atomic standards and
investigating other types, such as the hydrogen maser, which many
people feel is superior to the cesium standard. It is amusing to
note that the quartz-controlled oscillator has passed from something
which was avante garde for a primary standard to something which
is a consumer item, as contained in walkie-talkies that can be purchased
at many corner drugstores.
Unfortunately, the accuracy of the signal from WWV as received at
some distant point, typically 1,000 miles away, is considerably
poorer than that of the transmitted signal. This is indicated by
the dashed curve in Fig. 1. This deterioration of accuracy is due
to Doppler shifts resulting from motion of the ionosphere. The horizontal
slope of the latter portion of this curve indicates that the accuracy
of the received signals is ultimately limited by this effect. For
distant users the present frequency control of the station is far
better than it need be.
The NBS cesium beam atomic frequency standard NBS-with C. J.
Snider (left) and D.J. Glaze, W0YVZ
Howard E. Michel, Jr., K0BPY, checks the standing wave ratio
of the 15 MHz transmitter before turning on the power of the
10 kw. transmitter connected to the dummy load equipment shown
On the other hand, there are special
users who require these high accuracies, and many of them are located
at large distances. To satisfy their needs, other methods had to
be sought. One method is to use radio stations with much lower frequencies,
where propagation errors are far less serious. This approach led
to the establishment of WWVB and WWVL. Another approach is physically
to carry high-quality quartz clocks and small atomic clocks from
NBS and other reference laboratories to field sites. NBS and other
organizations are presently engaged in such an activity on a limited
The establishment of WWVB and WWVL was indirectly
assisted by the move of the principal radio work and some of the
low temperature work of NBS from Washington to new laboratories
at Boulder, Colorado, the home of the University of Colorado, during
1951-1954. At about that time the standards work and propagation
work were separated organizationally into the Radio Standards Laboratory
(RSL) and the Central Radio Propagation Laboratory (CRPL).3
A principal purpose of the move was to provide access to
better sites for propagation studies, and in due time experimental
standard-frequency transmissions with low power were commenced on
60 kHz from the Boulder site and on 20 kHz with an antenna strung
across Sunset Canyon, a few miles to the west. It was shown that
propagation errors at distances up to 2,000 miles were negligible
at 60 kHz. The 20-kHz transmission gives poorer accuracy at these
distances, but at distances above 2,000 miles its errors are less
than those of 60 kHz. However, should the accuracy of the frequency
standards improve by another factor of 10 greater than they are
today, it is almost certain that propagation errors at these two
frequencies will tend to limit the accuracy of the received signals,
and the carrying of clocks will play an even more important role.
As the result of the success of this experimental work, the
present stations WWVB and WWVL were constructed on a site approximately
seven miles north of Fort Collins, Colorado, which is known as the
home of Colorado State University. NASA provided the funds and sponsored
the WWVL facility, and is the main potential user of its signals
for synchronizing distant satellite stations. This site provided
a large area of flat land of very high conductivity, which aided
in improving the antenna efficiencies at these lower frequencies.
Also, it was far enough away from Boulder (56 miles) to avoid serious
interference to propagation studies from the high-powered transmitters.
The question arises: Why was it necessary to rebuild WWV if
these lower frequency transmissions give greater accuracy? The answer
is that it is a matter of convenience. This article is concerned
with WWV, and it would be inappropriate to give a long discussion
of the details of the construction of WWVB and WWVL and the methods
of using their signals. It suffices to say that most commonly-available
receivers cannot receive them at all, and if their signals are to
be fully utilized, special and rather expensive receivers are required.
The users who need the full accuracy, such as NASA, are very important
but are few in number, and are of a type that usually can afford
these special receivers. On the other hand, WWV and WWVH can be
received on sets which are generally available either without modification
or by the addition of a very simple converter. The number of users
whose needs can be met with the accuracy of WWV, using simple receivers,
is very large. Amateurs, of course, are in this group. Therefore,
it is considered justified to maintain and improve the service offered
to this larger group.
Modulation of WWV
Originally the WWV transmissions provided only standard radio
frequencies, with the principal purpose of making it possible for
radio stations to stay on their legally assigned frequencies. In
1935, the service was augmented by modulation of the carrier to
provide time pulses at one second intervals and standard musical
pitch. Later, other information - such as time, time-scale corrections,
and propagation warnings - was added to the modulation program,
as described in detail in Reference 1. Incidentally, signals from
WWV and WWVH may be partially distinguished, even though they are
on the same carrier frequencies, because the station announcements
are staggered and they have different silent periods (15 to 19 minutes
after the hour for WWVH and 45 to 49 minutes after the hour for
WWV). Propagation forecasts (mainly relevant to North Atlantic paths)
are given only by WWV, and are given after each station announcement
at five-minute intervals. They consist of a letter ("N" for normal,
"U" for unsettled, and "W" for disturbed) and a number from one
to nine to indicate the quality. Audio tones of 440 and 600 Hz are
transmitted on the schedule contained in Reference 1, where one
can also find explanations of other features which are of less interest
to most amateurs.
NBS Standards of Time and Frequency
The administration of WWV is related to the manner
in which the frequency of the station is controlled. Administratively,
the station comes under the jurisdiction of the Radio Standards
Physics Division, which, with a full-time staff of slightly more
than 100 people, is one of the two technical divisions of the Radio
Standards Laboratory. About one-half of the Division's staff, distributed
among three sections, is devoted to time and frequency matters (the
other three sections deal with radio materials, quantum electronics,
The Atomic Time and Frequency Section, headed
by Dr. James A. Barnes, has the responsibility of operating the
NBS Atomic Frequency Standards. The standard in use is a particular
cesium atomic beam built by NBS and referred to as "NBS III." However,
the cesium beam standard is a passive device, and the present one
is not designed to give automatic calibrations twenty-four hours
a day. Therefore, the Section also operates continuously five very
stable oscillators, some controlled by quartz crystals and the others
stabilized by atomic resonances. The frequencies of these oscillators
are continuously compared with each other, and the data are recorded
automatically. Also, once each working day they are compared to
NBS III. The output of one of the five oscillators is fed to a correction
device consisting of a driven phase shifter. The rate of drive of
the phase shifter is adjusted to (a) make output frequency correspond
to the average of the five oscillators (or, automatically, to the
average of four of them if the fifth one is in serious disagreement)
and (b) to correct for the average drift through aging of the oscillators.
The output of this correcting device is referred to as the Drift
Controlled Oscillator (DCO), and this serves as the basis for the
NBS time scales and for the control of the radio stations. Connected
to the DCO is also a device for producing the frequency offset required
by the NBS-UA Time Scale. Connected to these oscillators and other
circuits are a number of devices which count cycles and thus become
clocks for telling time on both the NBS-UA and NBS-A Time Scales.
Originally the epoch of the NBS-A Scale, which, unlike the Stepped
Atomic Time Scale (SAT) broadcast by WWVB, has never had any step
adjustments, coincided with that of UT on approximately January
1, 1958. At the present time, NBS-UA, which has been adjusted to
keep within close synchronization with the rotation of the earth,
lags NBS-A by about five seconds due to the irregular motion of
the earth, which during the immediate past has been slowing down.
Besides routine operation and maintenance of these devices,
the Atomic Time and Frequency Section also does fundamental research
and development of atomic frequency standards, and it possesses
several others of various types, partly for backup for NBS III and
partly for research purposes. An important part of this research
is the study of very-low-frequency noise. Additional important work
on atomic frequency standards is also carried out in the Quantum
Electronics Section, headed by Dr. Donald A. Jennings.
Control of the Radio Stations
The NBS radio
stations administratively are part of the Frequency and Time Broadcast
Services Section, of which Mr. David H. Andrews is Chief. The headquarters
of the Section is in Boulder.
The stations are controlled
by a system which makes direct reference to the NBS standards in
Boulder, and at the same time provides each station with high-quality
oscillators so that it can preserve a high approximation of synchronization
with the NBS III in case the control link fails for a time. Furthermore,
each station (counting WWVB-WWVL as one station for this purpose)
is equipped with three oscillators. On the assumption that it is
unlikely that more than one oscillator will fail or be in serious
error at one time, it is assumed that should one disagree with the
other two, those two can be considered as being correct. The new
Fort Collins WWV has three new commercially-manufactured cesium-controlled
The new WWV is located in a new building about
one-quarter mile away from the building housing the WWVB-WWVL transmitters,
but the two stations are integrally interconnected so that one person
can monitor all of the transmitters on the site and observe and
correct any equipment that malfunctions. Furthermore, although the
WWV and WWVB-WWVL frequency-control systems are nominally independent,
in the event of failure of one of them, switches can be thrown to
allow the remaining operating system to control all transmitters.
Also contained in the Fort Collins complex are spare devices for
generating frequency offsets.
The synchronization with the
NBS standards in Boulder is accomplished by the use of some monitoring
receivers located in Boulder and operated continuously. The received
signals are compared to a signal supplied from the DCO in the Atomic
Time and Frequency Standards Section, as mentioned above. Electronic
circuits determine the sign and magnitude of any frequency error,
and these control the modulation of a 49.85-MHz transmitter which
transmits the corrections to receivers at Fort Collins. Demodulating
circuits connected to these receivers generate correction voltages
which are applied to the oscillators that control the transmitters.
Thus, the system forms a closed-loop electronic servo, which not
only corrects for drifts in the oscillator, but also for changes
in phase resulting from swaying of the antennas in the wind. Incidentally,
local v.h.f. amateurs regularly use the signal from the 49.85-MHz
transmitter to check their 50-MHz receivers. However, in the near
future the 49.85-MHz link may be replaced by a microwave system.
Control of WWVH is accomplished primarily by monitoring the
WWVB and WWVL signals and correcting the oscillators. A check upon
the time synchronization is made occasionally by carrying portable
clocks, partly by NBS personnel and partly by others. It is the
aim of Mr. Andrews to have at least four clock-carrying trips made
to WWVH each year.
The Frequency and Time Dissemination Section,
headed by Mr. A.H. Morgan, does research on new ways of transmitting
frequency and, especially, time calibrations - for example, by the
use of satellites and the use of VHF meteor-scatter propagation.
It studies propagation errors for correction of the WWVB and WWVL
signals. It operates a number of receivers for monitoring both NBS
and some non-NBS standard frequency broadcasts. Comparisons are
continually made between the NBS standards and those elsewhere,
both in the U.S.A. and in foreign countries.
group in the Division Office, headed by Dr. George E. Hudson, also
has made important contributions to the time and frequency program
through representing the Division on important committees such as
the CCIR, in analyzing data, and in aiding in the determination
of frequency offsets and step adjustments.
As stated previously, Mr. David H. Andrews is Chief
of the section which administers the new station, and Mr. Peter
P. Viezbicke is the engineer in charge of the design and construction
of the new station. Mr. R.S. Gray served as an assistant to Mr.
Viezbicke during early construction. Mr. John B. Milton is in charge
of the design of the frequency-control system of the new station.
The writer could not have prepared this article without the
help of many individuals, especially many of those mentioned in
the article, in supplying information and checking the manuscript
for correctness. He is also indebted to Mr. Hugh J. Stewart for
help in obtaining the photographs; to Mr. Eldred C. Wolzien for
correcting the historical portions; and to Mmes. Donna Stolt and
Eddyce Helfrich for typing and editing.
During the last few
months of operation of the Greenbelt station, it was necessary to
have extra staff in order to man both the old and new stations.
During this period, much of the manpower at Greenbelt was supplied
under contract with the Philco Corporation by a staff headed by
Mr. W.M. Swartz.
NBS Miscellaneous Publication 236, "NBS Standard Frequency and Time
Services" (1966 Edition). For sale by Superintendent of Documents,
U.S. Government Printing Office. Washington, D.C., 20402 - Price
2 "Measures for Progress - A History
of the National Bureau of Standards, U.S. Department of Commerce,
3 In October, 1965, the organizational separation
was made much more complete when CRPL, although not moved geographically,
was removed from the jurisdiction of the National Bureau of Standards
completely and joined to a new agency of the Department of Commerce
called the Environmental Science Services Administration (ESSA).
At that time CRPL was renamed the Institute for Telecommunication
Sciences and Aeronomy (ITSA). It was joined by other organizations,
either removed to Boulder from elsewhere or newly created, to form
the Institutes of Environmental Research (IER) which is a major
unit of ESSA.