You are here

Nadir-Looking Synthetic Aperture Radar (NadirSAR)



The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 5.4.c.(8) of the solicitation.

OBJECTIVE: Develop very-high-resolution (as fine as 0.1 m) three-dimensional imaging techniques that will allow current and future Army microwave/millimeter wave synthetic aperture radars (SARs) to detect and identify targets in urban canyons, concealed under foliage, and other challenging environments using data collected with circular flight path trajectories.

DESCRIPTION: SAR is a principal sensor for collecting ISR data under all weather conditions and at all times of day from stand-off geometries. The Army currently has several microwave systems that provide valuable ISR information in open environments (i.e. environments in which the targets are not concealed under foliage or placed in areas containing many large structures). Conventional SARs fly straightline flight paths when performing their mapping functions.

Recently circular flight path SAR imaging techniques have been developed and demonstrated that can perform 360 deg imaging of targets, providing multiple aspect angle images of areas of interest that contain much greater detail than conventional, single look angle SAR images.

The objective of this topic is to extend the circular SAR imaging concept for imaging at very steep grazing angles (e.g. 70 to 85 degs). The objective of imaging at such step angles is to provide the SAR with the ability to peer into urban canyons and to penetrate some types of foliage by looking near-vertically through the branches instead of through the tree stems. For such imaging geometries, the cross-range SAR resolution remains that provided by the synthetic aperture length. However the range resolution will now provide target height information. The third dimension of range resolution, which would become a function of the elevation beamwidth of the antenna for the steep look-down geometry, must be achieved through an innovative processing technique. Such techniques could include the coherent processing of the circular trajectory data, tomography, interferometry, etc.

The microwave SARs that are currently used or that are being contemplated by the Army have only a single receive aperture. The algorithms and imaging techniques that are to be developed must be compatible with such systems. Also, while multiple orbits can be flown about an area of interest to form the NadirSAR images, operational constraints will favor those concepts that can provide the three-dimensional imagery in the minimum time.

Finally, there is currently no collected data available to support this effort. While the use of synthetic data is permissible, stronger research proposals would include data collections using SARs that can be made available and suitably modified for NadirSAR imaging.

PHASE I: The objectives of the Phase I program are to: 1) verify through simulation, analysis, etc., a concept for forming NadirSAR images, and 2) generate a Phase II program plan for simulating and/or collecting and processing the data. The Phase I effort should establish the fidelity of the simulation, the SAR parameters, the navigation requirements for the aircraft, and other such key factors relevant to the Phase II program.

PHASE II: The objectives of the Phase II program are to: 1) simulate and/or collect the NadirSAR data, 2) quantify the quality of the imagery that is formed (e.g. resolution, MNR, artifacts), and 3) demonstrate the ability to form three-dimensional SAR images of targets that are hidden in urban canyons, concealed under foliage, and placed in other challenging conditions. The demonstration of real-time imaging is not required.

PHASE III DUAL USE APPLICATIONS: NadirSAR should be a very useful capability for both military and civilian applications. The enhanced microwave SAR capabilities will allow military requirements such as detecting targets concealed under foliage to be achieved with existing systems, thus removing the need for additional, low-frequency SARs. Relatively minor modifications to existing equipment to support steep grazing angle imaging will probably only require minor hardware changes. Civilian support missions could include disaster relief (e.g. imaging rubble piles after earthquakes, searching for victims in forest and jungle areas), or detecting illicit/terrorist activities being conducted in challenging environments.


    • Cantalloube, H.M.J., "High resolution SAR imaging along circular trajectories”, Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International


    • Xiao Xiang Zhu, “Demonstration of Super-Resolution for Tomographic SAR Imaging in Urban Environment”, Geoscience and Remote Sensing, IEEE Transactions on (Volume:50, Issue: 8)


  • Carrara, Walter G. (1995) "Spotlight Synthetic Aperture Radar: Signal Processing Algorithms", Norwood, MA: Artech House

KEYWORDS: Synthetic Aperture Radar, Circular Imaging

  • TPOC-1: Jeffrey Spak
  • Phone: 443-861-1388
  • Email:
  • TPOC-2: Stephen Antunes
  • Phone: 443-861-1382
  • Email:
US Flag An Official Website of the United States Government