Question 6 Description of Research Project

0708-EX-PL-2015 Text Documents

Atmospheric & Space Technology Research Associates (ASTRA), LLC.

2015-11-06ELS_169126

                             ATMOSPHERIC & SPACE TECHNOLOGY
                                       RESEARCH ASSOCIATES, LLC
                              5777 CENTRAL AVENUE, Suite 221  BOULDER, COLORADO, USA 80301  303-993-8039

                                                  EIN: 20-2946717            DUNS# 60-1975803


Re: Application for New or Modified Station (Form 442),
    QUESTION 6: STATEMENT OF RESEARCH PROJECT

FCC Registration Number (FRN): 0015091481

To Whom It May Concern:

This letter is written in support of an application being submitted to the FCC, and provides a
brief narrative describing the statement of research.

The request is to operate one HF radio transmitter in Boulder, CO, to support HF Doppler
sounder systems measuring traveling ionospheric disturbances (TIDs) in the F-region of the
ionosphere in Florida and Hawaii. TIDs are wave-like corrugations in the ionosphere that
propagate from various sources including the aurora (northern lights), thunderstorms, and even
ocean waves.

The TID Detector Built in Texas (TIDDBIT) sounder systems provide crucial measurements of
TIDs. ASTRA’s TIDDBIT sounder is able to map the TIDs as they propagate, as depicted in
Figure 1 below.




 Figure 1. Reconstruction of isoionic contours perturbed by various TID components measured by the TIDDBIT
 TID Mapping System. Color scale represents height perturbation from – 7km to + 7 km. Left panel: horizontal
 distribution centered on TIDDBIT array (white dots) and extrapolated out to several hundred kilometers. Right
 panel: 3-D representation of left panel. Consecutive frames can be viewed as a movie showing TIDs propagating
 with time.


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Currently, we have similar transmitters set up in Florida and Hawaii, under FCC Licenses 0388-
EX-PL-2015 and 0394-EX-PL-2015, respectively. There are three transmitters at each project
site and one receiver that form a TIDDBIT system.

The TIDDBIT systems in Florida and Hawaii developed by ASTRA support both the Air Force
and Navy projects related to measuring and monitoring TIDs. The Florida TIDDBIT system
supports the operation of an Over The Horizon Radar (OTHR) in the Virginia area. The
reflection point of the OTHR is directly above Florida, and the TIDDBIT system serves to
monitor TIDs that can alter the reflection point, thus seriously degrading the operation and
performance of the OTHR. The Hawaii TIDDBIT system is part of a Navy sponsored research
program to monitor TIDs that may be coupled to ocean waves caused by tsunamis. These crucial
measurements of TIDs will lead to a better understanding of the link between tsunamis and TIDs,
and may lead to improved tsunami detection and warning techniques.

The proposed license would support these projects by setting up a transmitter locally in our office
in order to improve the remote systems, and we would test various transmitter components:
signal generators, amplifiers, and tuners.

We request permission to operate the experimental TIDDBIT transmitter in Boulder starting
December 1st, 2015 (or sooner), and will run for approximately 1 year. This allows us to
coordinate and improve with the TIDDBIT systems operating in Florida and Hawaii.

We have deployed and tested the system in Gainesville, FL, Mauna Loa, HI, San Antonio, TX (at
higher frequencies in the HF band), and also at Wallops Island, VA (at lower frequencies in the
HF band). It has worked reliably and collected good data. The radar was interfaced with a data-
logging computer, and a real-time display capability was developed and tested. Web-access to
the real time displays was also developed. This has been a major development over our previous
systems. It was required to enable operations and monitoring from a remote location. It also
allows a certain amount of ability to remotely modify and restart the system in the event of
software errors. The Web-access and real-time displays have allowed us to recurrently notice
and correct problems within hours of their occurrence, rather than the several days or weeks in
the past.


Brief Description of the TIDDBIT radar system:
One of the most sensitive methods for detecting transient changes in the ionosphere is the HF
Doppler sounder technique (Georges, 1967). A simple Doppler system consists of a continuous
wave (CW) radio transmitter and receiver, which are highly frequency-stable (1 part in 107),
together with some kind of recording device (e.g., Crowley, 1985). The CW signals are typically
transmitted in the HF band between 2-10 MHz. When a HF radio wave is reflected from the
ionosphere, movement of the reflection point during the passage of a TID produces a change in
phase path and a Doppler shift proportional to the time rate of change of the phase path.
Although the frequency shift is small (typically 1 part in 107), it can easily be measured by
comparison with a standard reference oscillator. A sensitive communications receiver with a
narrow bandwidth (~100 Hz) receives the sky-wave signal at a site about 50-100 km from the

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transmitter and down-converts the signal to a frequency of several Hertz. The Doppler shift of
the received signal is thus measured from variations of the receiver output frequency. If three
transmitters are used, the spatially separated propagation paths can be monitored, and the time
difference between the wave signatures from the three reflection points yields the speed and
direction of the TIDs by triangulation.


Transmitter:
Each of the three HF transmitter systems consists of a signal generator feeding a CW signal into
a HF amplifier. The amplifier output then feeds a simple dipole antenna, which is installed in an
inverted-V configuration. Thus the major lobe of the antenna radiation pattern is in the vertical
direction. Because we need to recognize the three transmitted signals at the receiver, frequency
offsets of 10 and 20 Hz are applied in two of the transmitted CW signal frequencies. Thus, if one
transmitter operates at a frequency of 4.62 MHz, the second would operate at 4.620010 MHz,
and the third would operate at 4.620020 MHz.
        Antenna Height is less than 6 meters.
        RF output power at the transmitter terminals is 50 Watts.
        Mean Max Effective Radiated Power is ~82 Watts.
        FCC Emission type is N0N.

       Necessary Bandwidth: the transmitted signal only occupies at most 35 Hz of spectrum.


Receiver:
The receiver system consists of 4 Ten-Tec 331 receivers. The radar will operate on two
frequencies, and both O- and X-modes will be differentiated, so four distinct channels will be
analyzed in the system. The baseband audio (with BFO of 1 kHz) outputs from the receivers into
an 8-channel A/D converter (only 4 channels are used) and is processed on a PC. The processed
data is logged on a large hard drive for Doppler-data processing. The antenna feeding the
receivers is a crossed inverted V dipole (less than 6 m tall) with a quadrature hybrid to separate
O- and X-mode components. A highly stable 10 MHz oscillator is used to stabilize the receiver
system.

A typical data set is shown in Figure 2, which shows the Doppler shifts caused by well-correlated
TIDs perturbing the radio reflection points on three different transmission paths at different times
for October 15th, 2006. Time delays between the perturbations on different Doppler paths have
traditionally been estimated by the cross-correlation technique, however we developed a cross-
spectral analysis technique, which has the advantage of separately examining the time (i.e. phase)
component of a signal (Crowley et al. 1984; Crowley 1985).




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           Figure 2: TIDs measured by TIDDBIT system on three propagation paths.


Rationale for Transmitter Site Selection:
Currently, we have similar transmitters set up in Florida and Hawaii, under FCC Licenses 0388-
EX-PL-2015 and 0394-EX-PL-2015, respectively. There are three transmitters at each project
site.

We would like to set up a transmitter at our Boulder, CO, office to test various transmitter
components in order to improve the transmitters currently set up in Florida and Hawaii. The tests
would include experimentation with signal generators, amplifiers, and tuners. The effective
radiated power would not exceed 82 W.


Rationale for Frequency Selection:
We have used the International Reference Ionosphere (IRI) model to predict the ionospheric
conditions near Boulder, CO, during the coming year. Ideally, we would like to use two
frequencies that reflect off the ionosphere at an altitude greater than 150 km, and we would like
the altitude separation between these two frequencies to be greater than 20 km (in order to obtain
vertical wave information).

Given that the ionosphere changes significantly throughout the day and with month of the year,
we would like to pick 2 frequencies that give us the greatest amount of time to provide useful
scientific data over the course of a year. We have conducted a trade study to determine the
optimal frequencies, and this information is summarized in Figure 3.




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Figure 3: Optimization analysis for frequency selection. The color represents the percent of time
  that the two frequencies can provide robust scientific data for the duration of the experiment.
    The green dashed box shows the requested frequencies from two bands in Fixed Mobile.

In this figure, the first selected frequency is on the x-axis, and the second selected frequency is
shown on the y-axis. Each axis is also labeled with the relevant primary user group. The color
represents the percent of usable time that we would obtain useful TID information on both
frequencies, and ideally we would like this to be 100%. Unfortunately, the maximum value in the
graph is 80%, and it falls in a range of frequencies set aside for Maritime Mobile and
Broadcasting, which are therefore not available for our use.

For the proposed experiment, we request permission to operate at frequencies in the Fixed
Mobile bands, and here we see a maximum of ~70% for f1 between 4.438 and 4.650 MHz, and
for f2 between 6.765 and 7.000 MHz (green dashed box in Figure 4). Therefore we are
requesting permission to transmit at frequencies within these two bands:

       Fixed Mobile: 4.443 MHz
       Fixed Mobile: 4.647 MHz
       Fixed Mobile: 6.769 MHz
       Fixed Mobile: 6.993 MHz

Also, we would like to use similar frequencies to mimic our HF sounder systems in Florida and
Hawaii.



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Please contact Dr. Geoff Crowley at ASTRA with any additional questions.

Your help in approving this application would be much appreciated.

Sincerely,

Dr. Geoff Crowley
President | Chief Scientist
ASTRA, LLC
5777 Central Ave, Suite 221
Boulder, CO 80301
(303) 993-8039
gcrowley@astraspace.net
www.astraspace.net




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Document Created: 2015-11-06 09:16:18
Document Modified: 2015-11-06 09:16:18

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