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)

HF DOPPLER SOUNDER ARRAY

F-Region Ionosphere

200-400 km

3-10 MHz

Tx

Rx

TxTx

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

Rx

1

2

3

TIDDBIT Radar at Wallops Island

Rocket

Wallops Island IRI Sept 1, 2006

TIDDBIT Data Depends on Propagation Conditions

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

Observed TID Spectra

Measures Acoustic waves (τ ~ 1 min) to Large Scale TIDs (τ ~ 4 hrs)

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)

Quiet Day Wave Propagation (1/30/2002)

Wave periods 30 min – 4 hr. Wave periods 10 – 45 min.

Active Day (2/6/2002)

Wave velocities for periods of 10 – 45 minutes.

Quiet Day (1/30/2002)

Wave velocities for periods of 30 minutes – 4 hours.

Active Day (2/6/2002)Quiet Day (1/30/2002)

QUIET DAY

STORM DAY

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)

100 km

50 km

Tx-1

Tx-2

Tx-3

Rx

TIDDBIT Radar Planned for Jicamarca

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

TIDDBIT Radar in New Mexico

25 km

50 km

75 km

Value of Deploying a 2nd system around Socorro

100 km

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