This project focused on subsurface remote sensing for unexploded ordnance (UXO) discrimination in highly contaminated environments. “Highly contaminated” can refer to the density of UXO, clutter, or both. Three scenarios were targeted for investigation:

1. Fragment cloud: many small metallic non-UXO items together, which must be distinguished from a target of interest;
2. The screening problem: a single UXO-sized object beneath or among a distribution of smaller clutter fragments;
3. Few sizeable objects: two UXO-sized objects in close enough proximity that their sensor signals overlap spatially.

The technologies applied were ultra-wideband (UWB) electromagnetic induction (EMI) sensing and UWB fully polarimetric ground penetrating radar (GPR). These were used separately to investigate the characteristics and performance of each; and together to investigate where the two technologies, with some innovative processing, might be complementary.

GPR was largely immune to problems caused by smaller near-surface metallic objects, but suffered signal clutter from soil heterogeneity.  While less soil sensitive, EMI was substantially hindered by discrete or dispersed near-surface clutter, with some apparent discrimination advantage from elevating the sensor.  GPR helped suppress EMI false alarms in blind tests.

A new, faster GPR system incorporating the advanced digital down converter (DDC) and direct digital frequency synthesis (DDS) technology suitable for UXO detection/classification was developed. This radar system is able to cover a frequency range from at least 10 MHz to 810 MHz by sweeping the frequency at 4 MHz increments, which is suitable for UXO detection/classification. The new frequency source design is adopted using a high-speed direct DDS chip by Euvis DS852 and DS853. The new design reduces the collection time by a factor of three compared with the network analyzer. It takes 0.3 seconds for 201 frequency sweeps with the new system.

The GPR operating software (GPROS) has also been developed based on the graphical user interface (GUI). This operating system enables user control of the new radar system include including DDC, DDS, and the automatic triggering system and provides a simple data processing tool such as the inverse fast Fourier transform (IFFT), waterfall plot, slope gain adjuster, and band-pass filters.

The new, miniaturized UWB dual-polarization horn fed bowtie (HFB) antenna was designed to improve the mobility and the spatial resolution by reducing size and weight of the antenna. The antenna is properly operated in the frequency range for the UXO detection (30 – 810 MHz) and provides the dual polarization feature. To reduce reflection from the end of the antenna, a lump resistances (120 Ω) were loaded between the end of each arm and the ground cavity. The size of the new antenna is 2.5 times smaller than that of the conventional UWB HFB in the same operating frequency range. Performance of the new miniaturized UWB HFB antenna is similar to the conventional UWB HFB antenna in terms of the target response, while the new antenna has better mobility and spatial resolution.