Extraction of landmine signature from ground penetrating radar signal

With its principle of detection based upon electromagnetic (EM) wave propagation parameters inhomogeneities within the medium under consideration, ground penetrating radar (GPR) is poised to be a very valuable tool in the field of humanitarian demining, especially for the detection of plastic landmines. In this regard, however, its performances strongly depend upon the EM properties of the medium surrounding the target, and upon the dielectric contrast between the target and the surrounding medium. After a short introduction to the world landmine problem, this article presents the extraction and modeling of buried targets signatures from a stepped-frequency continuous wave GPR signal. The signal is decomposed in its soil and targetin-soil contributions. The mine signature extraction process is detailed, and the outline of the GPR model used to simulate these signatures is also presented. More importantly, the reasons for mine signature extraction and simulation are discussed. This development is completed by the validation of the numerical model, which shows encouraging results for the path of research. I. MINE FACTS AND FIGURES The following figures can be found at the following adresses: www.state. gov/t/pm/wra/ and www. cirnetwork.org/info/fact_sheet. cfm. A. Mines by the numbers Landmines • are estimated to be 45-50 million infesting at least 12 million km of land • affect more than 100 countries • heavily affect 20 countries: Angola, Afghanistan, Croatia, Egypt, Cambodia, . • kill or maim a reported 10,000 people annually (UNICEF: 30–40% of victims are children of 15 or less) • cost US$3–30 the unit. B. Heavy economical impact Landmines • create millions of refugees • prevent hundreds of thousands of km of agricultural land from being used • deny thousands of km of roads for travel • create food scarcities, causing malnutrition and starvation • interrupt health care, increasing sickness and disease • inflict long-term psychological trauma on landmine survivors • hinder economic development • undermine political stability. C. Demining: a slow/costly process Demining process • is extremely dangerous: 1 accident/2,000 mines destroyed • costs US$300–1,000 the unit • is slow: ∼100,000 mines/year cleared. So there is a real need for a faster, cheaper and more secure demining process. It includes, but is not limited to: • improve currently used detectors • increase research on new technologies The list of currently available detectors and prototypes is presented at table I. II. RADAR SYSTEM DESCRIPTION We use a stepped-frequency continuous wave (SFCW) radar becauses it possesses several advantages over the time domain technology [1], among which: • possible to control the signal over a very large bandwidth (0.75–4 GHz) • ease of characterization of the elements of the system (cables, antenna) TABLE I LIST OF CURRENTLY AVAILABLE DETECTORS AND PROTOTYPES. sensor type sensor maturity effectiveness prodders & acoustics prodder in use high acoustic R&D high (wet soil) EM MD in use very high GPR R&D/in use high (dry soil) MWR R&D medium biosensor dog in use medium–high rodent in devel. medium–high nuclear all prototype — chemical all prototype — • better signal-to-noise ratio (SNR) than for time-domain GPRs. The antenna is used off-ground and has the following features: • TEM horn (high directivity) • used in monostatic mode (simpler modeling, shorter round-trip path). The radar system is emulated by a vector-network analyzer (VNA). The measured signal is S11(ω). III. RADAR SYSTEM MODELING The signal measured by the radar is the sum of two contributions: S total 11 = S 11 + S target 11 (1) which can be rewritten using a transfer functions formalism as (Fig. (b); Hm is neglected): S total 11 = Hi + H (Gs + Gt) (2)