The Radiation Laboratory The Radiation Laboratory Outline Motivation

The Radiation Laboratory

The Radiation Laboratory Outline: Ø Motivation ØDetection of targets camouflaged under foliage using multi-frequency, -polarization, -incidence angle SAR/INSAR sensors. Ø Physics-based scattering and propagation modeling of clutter Ø Model reduction (extraction of channel parameters) Ø Scattering models for hard targets under trees Ø High resolution SAR/INSAR image simulator Ø 3 -D SAR at MMW for target detection and identification

The Radiation Laboratory Motivation Ø A reliable approach for detection and identification of targets camouflaged under foliage with an acceptable false alarm rate and probability of detection has not yet been developed. Ø Due to the complexity of the problem, i. e. ØSignal attenuation, phase-front distortion, poor signal-toclutter ratio, etc. , single sensor approaches (optical, IR, radar) do not produce satisfactory results. Ø “Capable sensors” operating in diverse modality in conjunction with novel algorithms can drastically enhance FAR and PD. ØPolarization diversity, Multi-frequency, Multi-static, Multiincidence angle, Interferometric

The Radiation Laboratory Phenomenology of Wave Scattering & Propagation In Forest ØForest is a complex random medium composed of lossy scatterers Satellite arranged a semi-deterministic ØFoliage cause significant attenuation, scattering, field fluctuation ØTo assess performance of radar sensors and target detection algorithms phenomenology of EM wave interaction with foliage must be understood. Ø Scattering from foliage (clutter) Ø Target is in the close proximity of many scatterers UAV ØDistortion of phase front and the scattered field from target Ø Signal level, fluctuations, polarization state, impulse response, spatial coherence etc. depend on: Ø Tree density Ø Tree type Ø Tree height and structure receiver

The Radiation Laboratory 3 D Tree Generation Ø Lindenmayer systems allow generation of complex tree structure using only a few parameters Ø An algorithm based on self-similarity Tree structure G = G(V, , P) Axiom = X Productions: p 1: X FF{-X}F{++X}F{+X}{-X} p 2: F FF Ø Gross structure: columnar, excurrent, decurren Ø Biophysical parameters include tree height, trunk diameter(dbh) and branching angle

The Radiation Laboratory • Tree Type: Coniferous and Deciduous • Inclusion of Botanical Information – Tapering in Length and Diameter *Law of conservation of cross section area r 0 2 = r a 2 + r b 2 – Stochastic Processing – Leaf Arrangement Red Maple rb ra r 0 • Computer Implementation – Tree DNA generation and structure visualization • Forest stand generation and visualization (scaling and view angle) Red Pine

The Radiation Laboratory Put Matts stuff here Fractal tree details GUI Still scenario Movie Tree generation graphical user interface The Radiation Laboratory

The Radiation Laboratory ØLand cover ØDEM ØTree stand placement ØVehicles, transmitter, and receiver placement Scene Generation and Visualization

Propagation & Scattering Model for Forest Canopies • Scattering from discrete scatterers - Trunk: stratified dielectric cylinder - Branch: homogeneous dielectric cylinder - Leaf: dielectric disk or needle - Ground: layered dielectric half-space • Single Scattering is invoked • Four Scattering Mechanisms are included Height The Radiation Laboratory Rough Interface Attenuation rate NP/m

The Radiation Laboratory Source or Observation Point in the Forest Ø Near-field calculation is required Ø Approximate analytical formulations for near-field scattering from branches and tree trunks are derive. Ei Ø Coherent summation of scattered field from all tree components. (Coherence is important at S-band lower) Es Ed Er Single scattering theory Interaction among tree structures are ignored.

The Radiation Laboratory

Backscattering Coefficient of Red Pine Forest The Radiation Laboratory Red pine 150 trees & 100 realization. Tree height: 15. 3 m Density: 0. 1/m 2 Crown Height: 9. 5 m 45

Time-Domain Response at a FDTD Grid Point The Radiation Laboratory Frequency: 30 MHz – 100 MHz 10 trees are considered. Dielectric constants: 21. 7 + i 14. 6 for branch 9. 8 + i 1. 7 for ground. Height of tree: 15 m, Diameter of trunk: 22 cm. 45 o Incidence angle. attenuation dispersion attenuation Note: Small effect of forest

The Radiation Laboratory Time-domain Response Observation point is 1 m above the ground inside a pine forest. v-pol. wave is incident at 40 o, and BW 1 GHz (1 GHz – 2 GHz). Ez V/m Ez Severe distortion due to trees & Dispersion Time[ns]

The Radiation Laboratory Interaction of Foliage and Target Hybrid Frequency/Time-Domain Simulations 1. Using the forest model, calculate time domain response of several trees in the proximity of the target at FDTD grids on a box (excitation). h-pol. or v-pol. 2. Using FDTD, compute scattering from the target on the same grid points. including all interactions

The Radiation Laboratory Hybrid Frequency/Time-Domain Simulations (Cont. ) 3. To calculate the interaction between the target and the forest, reciprocity theorem is used. After exchanging observation & source points, use the previously calculated scattering property of the forest to obtain the final backscattering result. Observation point exchanging Source point Note: Using this procedure, interaction between forest & target is taken account into up to first order.

Validation of Hybrid Frequency/Time-Domain Modeling The Radiation Laboratory A FDTD box around the observation point Validation A 2 x 2 x 2 FDTD mesh is used to model free space within the forest (in the absence of any vehicles). The same problem is solved by a pure Mo. M code. Results of the two methods are in excellent agreement. (x) (y) (z) 2 x 2 x 2 FDTD mesh and electric field component that is plotted in the figure on the right. FDTD simulation parameters : Dx = Dy = Dz = 0. 3 m Dt = 0. 314 nsec

The Radiation Laboratory Discretized HUMVEE for FDTD Analysis Ei z x y 400 Bistatic Scattering From HUMVEE

The Radiation Laboratory Preliminary Results Current Distribution over the HUMVEE

Field Distribution On the FDTD Box(2 GHz) The Radiation Laboratory h-pol. incidence v-pol. incidence Note : Considerable distortion due to trees.

The Radiation Laboratory l Macromodeling of Field Statistics – Mean Field at receiver is of the form: l. Functional to macromodel mean field should be of similar form such as Prony’s exponential series expansion: l. According to Foldy’s approximation a direction, remembering: < S > in forward

The Radiation Laboratory Pine Forest - Mean Field i = 45 o <EThy> Simulated Data Macromodel Prony’s order = 3 <ETvx> <ETvz>

The Radiation Laboratory Model reduction: Field STD Standard deviation is a smooth function of f l It is therefore possible to macromodel the standard deviation with a functional in the form of a Taylor series polynomial: l std(Etvx) std(Ethy) std(Etvz)

Model Reduction: Spatial Correlation The Radiation Laboratory Spatial Correlation v-pol. h-pol. 1 1 Calculated 1/(1+ ax) 0. 8 a = 1. 58 0. 8 a = 1. 07 0. 6 0. 4 0. 2 0 0 -5 0 l Observation line 5 -5 0 5 l Note: Since observation line is inside the shadow region, field should be highly correlated.

The Radiation Laboratory VV Polarization Michigan SAR Image Simulator Geometry HH Polarization Increasing Range Direction of Flight 0 d. Bsm Point Target

The Radiation Laboratory Future Works 1. Use physics-based model for generating synthetic multimodal data • Statistics of clutter scattering and channel (Monte Carlo simulations) • Hard target interaction with foliage (model reduction) 2. Improvement of Forest Model Accuracy • Including the effects of near-field multiple scattering among vegetation components. 3. Hard target model reduction (scattering centers) 4. Implement hybrid foliage/hard target interaction. 5. Improve computation time: Parallel processing

The Radiation Laboratory 50 Km X-band 225 Km C-band Swath Width Shuttle Radar Topography Mission