The TIDDBIT HF Doppler Radar
G. Crowley and F. RodriguesAtmospheric & Space Technology Research Associates
(ASTRA)
Abstract: HF Doppler sounders represent a low-cost and low-maintenance solution for monitoring gravity wave activity in the F-region ionosphere. HF Doppler sounders together with modern data analysis techniques provide both horizontal and vertical velocities across the entire TID spectrum. ASTRA has extensive experience with HF systems, and is currently building Doppler sounders in Texas, Virginia, and Peru.
(TIDDBIT = TID Detector Built In Texas)
HF DOPPLER SOUNDER PRINCIPLE
F-Region Ionosphere
200-400 km
3-10 MHz
Tx Rx
Radar Principle
f = -1/ (dP/dt)
dP can be caused by:a) changes in reflection heightb) changes in refractive index (electron density profile)
TYPICAL RADAR SPECIFICATIONS
3 Transmitters, Single Receiver
Spacing: 50 – 300 km
Dual Frequency (Altitude separation)
CW system
Advantages:
Power: 20-100 W
Continuous
30 sec cadence
Rx
Tx
Tx
Tx
Scale: 50 – 300 km
X
X
X
The TIDDBIT array has baseline dimensions of 140 x 210 km, ideal for TID studies.
Original TIDDBIT Array in Texas
Typical Doppler DataTypical Doppler Data
TIDs on three propagation paths for 4.5 MHz sounding frequency on January 30th, 2002
Gravity Waves – An Introduction
Growth with Altitude
V2
Waves Everywhere!
Sources: Aurora Weather Fronts Thunderstorms Topography & winds
Explosions
Restoring Force
Acoustic Waves - Pressure
Gravity Waves - Gravity
Measures Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs)
Classification of Gravity Waves/TIDs
Medium Scale Large Scale
Period 10-30 min 0.5-5 hr
VH (m/s) 50-300 300-1000
H (km) 100-300 300-5000
Measures Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs)
TID Parameters Provided by TIDDBIT radar
TID Accurately Represents Underlying
Gravity Wave Properties?
Wave Period YES
Horizontal Phase Trace Speeds (as fctn of period)
YES
Vertical Phase Trace Speeds (as fctn of period)
YES
Horiz. & Vertical Wavelengths (as fctn of period)
YES
Spectrum (Wave Amplitude as function of Period)
Requires Calibration
Measures Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs)
1. Detrend the data2. Calculate Variance3. Perform FFT4. Compute the Period1. Take input from two stations.2. Perform cross-spectral analysis3. Compute relative time delays
1. Test to see if data is usable for horizontal velocity
calculation (based on coherency).2. Determine the two largest coherencies3. Compute 95% confidence intervals based on
coherencies4. Call separate subroutine for each pair.5. Take relative times and compute velocity
and azimuth for station configuration.
Peak Detection
Raw Data
FFT Calculation
1. Calculate mean and standard deviation for each peak range.2. Find values above threshold (set in number of standard deviations from the mean).3. Calculate equation parameters for Gaussian curve with IDL gaussfit routine.4. Calculate peak values with equation parameters. 5. Get Chi-squared value.
Delays Calculation
Horizontal Velocity
Horizontal Phase Trace Speed
Horizontal Azimuth
1 hr30 min
1 hr30 min
500
0
Measures Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs)
Azimuth versus Local Time (Oct 11-26, 2006)
Local Time
Period = 30 minH
oriz
Azi
mut
h (
ºE o
f N
)0
90
180
360
270
TIMEGCM Wind Azimuth
Horiz. Phase Speed versus Local Time (Oct 11-26, 2006)
Period = 30 min
Local Time
Hor
iz P
hase
Tra
ce S
peed
( m
/s)
TIMEGCM Wind Speed
Deriving Horizontal Thermospheric Winds from Gravity Waves
From Vadas and Fritts (2005):
Given GW wave-vector and background neutral parameters, one can try to solve for UH !
First successful attempts made with multi-beam ISR observations (Vadas and Nicolls, 2008)
C/NOFS-RELATED SCIENCE STUDIES
• Possible Triggers for Instability generation
TID Studies
Spectral Morphology
Underlying Wave Characteristics
Effects of Waves
Separation of triggering mechanisms
• E-field measurement capability
Continuous measurement of iso-ionic contour drifts
ConclusionsConclusions Successfully built and operated TIDDBIT radar. Continuous operation: 2002, January - April
2005, Jan - May Successfully developed end-to-end data analysis. Complete description of TID characteristics: Period, VH,
VZ, λH, λZ, as a function of τ. Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs) Day-to-day variability in TID characteristics. Developed real time displays Deployment near Wallops (July 2006) Continuous operation: 2006, July-Sept Continuous operation: 2007, Aug-Nov Partial deployment in New Mexico: June 2008 Deployment at Jicamarca, Peru – Oct 2008 C/NOFS – TIDs, Triggers of ESF, E-fields Gravity wave propagation/raytracing studies
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