Feasibility Study for Reconstructing the Spatial-Temporal Structure of TIDs from High-Resolution Backscatter Ionograms Dr. L. J. Nickisch, Dr. Sergey Fridman, Dr. Mark Hausman NorthWest Research Associates, Monterey, California Dr. Geoffrey S. San Antonio Naval Research Laboratory, Radar Division Presented at the 2015 Ionospheric Effects Symposium 12 May 2015 1
Motivation • Medium-scale TIDs can cause large geolocation errors for over-the-horizon (OTH) radar – Apparent target location swings of tens of kilometers in 5-10 minutes • ROTHR-Virginia return from stationary 80 km Azimuth transponder in Jamaica Time duration: 2.5 hours 2
Motivation (cont.) • OTH radars routinely collect backscatter soundings – Wide Sweep Backscatter Ionogram (WSBI) – Surface clutter returns as a function of delay and transmission frequency for a span of azimuths • Can information from WSBIs be used to infer TID structure in real time? 3
GPS Ionospheric Inversion (GPSII) • The algorithm can assimilate diverse TEC-related data obtained on transionospheric propagation paths – GPS L1/L2 beacon signals ⇒ GPSII > Dual frequency group delay data (absolute TEC) > Dual frequency phase delay data (relative TEC) – TEC data obtained with LEO beacons – Occultation-type oblique TEC from space-based receivers (CHAMP, COSMIC, DORIS) • Other data types – Vertical/Oblique soundings (especially important for HF skywave applications) – HF backscatter soundings – On-board plasma density measurements from satellites (such as CHAMP, DMSP) – Doppler sounding data 4
The Ionospheric Reconstruction Problem: Tikhonov Method = u ( , t ) r N ( , t ) N ( , t ) e r r 0 { } = U { u ( , t )}, Biases r ≈ Y M [ U ] Y is the set of measured absolute/relative TEC values and data points from other types of ionospheric measurements. The solution must fit the data within − − − ≤ T 1 ( Y M [ U ]) S ( Y M [ U ]) dim( Y ) 1 errors of measurements. Error covariance matrix There are infinitely many such solutions: − U → U T 1 P min The smoothest solution is selected by minimizing the stabilizing functional Pseudo-covariance matrix -The pseudo-covariance P matrix is defined in such a way that the stabilizing functional tends to take on larger values for unreasonably behaving solutions (“reasonable” “smooth”). -The nonlinear optimization problem is solved iteratively (Newton- Kontorovich). 5 5
Synthetic Wide-Sweep Backscatter Ionogram Generated by NWRA HiCIRF code 6
Real OTHR Backscatter Ionogram Encompasses ~10 ° azimuthal swath 7
Can WSBI leading edge structure be assimilated to expose TIDs? • ROTHR WSBIs are collected using only the end 28 elements of its 372 element receive array – Yields ~10 ° azimuthal resolution Use of full aperture would allow WSBIs with ~1 ° spacing • – Allows detection of leading edge TID structure • Assimilating WSBI leading edge data would be an excellent way of mitigating TID effects on OTHR CR – WSBIs are routinely collected by OTHR – WSBIs densely sample the OTHR operational field of view – Modern digital technology will allow next generation OTHR to collect WSBIs using the full receive aperture without impacting the surveillance mission of the radar • Full-aperture WSBIs were collected on ROTHR by Dr. Geoff San Antonio (NRL) in an experimental configuration of ROTHR 8
High-Resolution Leading Edge Data Color contours span 15 (blue) to 27 (red) MHz WSBI Leading Edge as Function of Frequency 4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 Full aperture WSBI leading Simulated WSBI leading edge measurements edges using NWRA ray collected by Dr. Geoffrey tracing in TID model San Antonio (NRL) 9
The Hooke TID model was incorporated into NWRA’s ray tracing code • Hooke, W. H., “Ionospheric irregularities produced by internal atmospheric gravity waves,” Geophysical Monograph Series, The Upper Atmosphere in Motion , Vol. 18, pp. 780-808, 1968 10
Generated synthetic high-resolution WSBI leading edge data: Known truth data 15JAN14-1900 Leading Edge 10-24 MHz Blue → Red 34 32 30 28 26 Latitude 24 22 20 18 16 -90 -85 -80 -75 -70 -65 -60 Longitude 11
Modified GPSII to assimilate hi-res leading edge data ∆ π ∆ t − 2 t = γ + γ + ν γ = τ U U U 2 e cos − − n 1 n 1 2 n 2 n 1 T ∆ t − − 2 2 x x ∑ ∆ ∆ τ γ = − = t t i − e s − F ( x ) f v + α α τ 2 − τ γ = + i x x f e e s α = − + 1 i 1 i 1 ∆ ∆ t t − − τ τ γ = − e s f 1 − + − 3 2 2 ( t 2 t t ) + d ( 1 d ) − + − − − d 1 d 1 d d 1 d − + + − − + − − + + − + 3 2 ( 2 ) t ( 3 2 ) t t 1 + + − + − 1 d d d 1 d d 3 2 2 t t t = + − − + − v ( t ) − − − [ 1 : 2 ] − + 3 2 d d 1 d d 1 d 1 3 t 5 t 2 − + − + + + − − − + + − = 3 2 ( 2 ) t ( 3 2 ) t t v ( t ) − + + + [ 1 : 2 ] − + + 3 2 2 3 4 1 d d 1 d d 1 d t t t − + − + − − 1 3 2 t t − 3 2 ( t t ) + d ( 1 d ) + + − − − = ∑ ∑ ∑ 2 2 2 y y x x z z j x i y z k F ( x , y , z ) f v v v + α + β + γ α β γ − − − i , j , k x x y y z z γ = − β = − α = − + + + 1 1 1 i 1 i j 1 j k 1 k ≤ < ≤ < ≤ < x x x , y y y , z z z + + + 1 1 1 i i k k k k 12
Sample Input Data 15JAN14-1920 Leading Edge 10-24 MHz Blue → Red 15JAN14-1924 Leading Edge 10-24 MHz Blue → Red 15JAN14-1928 Leading Edge 10-24 MHz Blue → Red 34 34 34 32 32 32 30 30 30 28 28 28 26 26 26 Latitude Latitude Latitude 24 24 24 22 22 22 20 20 20 18 18 18 16 16 16 -90 -85 -80 -75 -70 -65 -60 -90 -85 -80 -75 -70 -65 -60 -90 -85 -80 -75 -70 -65 -60 Longitude Longitude Longitude 15JAN14-1932 Leading Edge 10-24 MHz Blue → Red 15JAN14-1936 Leading Edge 10-24 MHz Blue → Red 15JAN14-1940 Leading Edge 10-24 MHz Blue → Red 34 34 34 32 32 32 30 30 30 28 28 28 26 26 Latitude Latitude 26 Latitude 24 24 24 22 22 22 20 20 20 18 18 18 16 16 16 -90 -85 -80 -75 -70 -65 -60 -90 -85 -80 -75 -70 -65 -60 -90 -85 -80 -75 -70 -65 -60 Longitude Longitude Longitude Samples separated by 4 minutes in time spanning 20 minute period of TID 13
Sample Output: Plasma frequency (MHz) at 250 km altitude 14
Comparison of Output to Truth Output Truth 15
Future plans • Result of synthetic feasibility study is encouraging • This work will continue over the next two years – Collect full aperture WSBI data on ROTHR in conjunction with fixed transponder data – Add capability for assimilating surface clutter Doppler data – Field and ASTRA TIDDBIT system in the field of view of ROTHR to collect independent TID data for comparison (Dr. Geoff Crowley) 16
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