{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T15:23:59Z","timestamp":1788967439955,"version":"build-2803163510"},"reference-count":37,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T00:00:00Z","timestamp":1788912000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100009917","name":"U.S. Naval Research Laboratory","doi-asserted-by":"publisher","award":["996D45"],"award-info":[{"award-number":["996D45"]}],"id":[{"id":"10.13039\/100009917","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100009917","name":"U.S. Naval Research Laboratory","doi-asserted-by":"publisher","award":["62A1B5"],"award-info":[{"award-number":["62A1B5"]}],"id":[{"id":"10.13039\/100009917","id-type":"DOI","asserted-by":"publisher"}]},{"award":["996D45"],"award-info":[{"award-number":["996D45"]}],"id":[{"id":"https:\/\/ror.org\/03cs53d16","id-type":"ROR","asserted-by":"publisher"}]},{"award":["62A1B5"],"award-info":[{"award-number":["62A1B5"]}],"id":[{"id":"https:\/\/ror.org\/03cs53d16","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>This paper describes a polarimetric, frequency-modulated continuous wave (FMCW) synthetic aperture radar (SAR) with an ultrawide bandwidth that spans 2\u201318 GHz. It is being developed as an airborne sensor called SKuSAR. The intent is to generate a set of sub-band images, thereby creating a multispectral SAR. This opens the prospect for new remote sensing algorithms that exploit variations in the scene\u2019s polarization\/frequency response occurring over the system\u2019s three octaves of bandwidth. We describe the SKuSAR hardware and the processing steps applied to the FMCW data to create a multispectral SAR. The approach is practically demonstrated using data collected against calibration targets deployed in a field with the system mounted on a truck. This ground-based arrangement provided an inexpensive solution to test and fine-tune the system hardware and processing algorithms. A few complicating factors specific to the ground-based geometry were encountered, such as multipath signal contamination due to ground reflection and rather short data collections that affected attainable azimuth resolutions. Both these factors were identified and analyzed. The measured characteristics follow theoretical predictions rather well, giving confidence that the system meets its expected nominal performance once airborne, with the mentioned limiting factors absent or of reduced significance.<\/jats:p>","DOI":"10.3390\/s26185737","type":"journal-article","created":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T15:01:56Z","timestamp":1788966116000},"page":"5737","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Demonstration of a 2\u201318 GHz Multispectral SAR"],"prefix":"10.3390","volume":"26","author":[{"given":"Mark A.","family":"Sletten","sequence":"first","affiliation":[{"name":"U.S. Naval Research Laboratory, Remote Sensing Division, Washington, DC 20375, USA"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0474-6470","authenticated-orcid":false,"given":"Jakov V.","family":"Toporkov","sequence":"additional","affiliation":[{"name":"U.S. Naval Research Laboratory, Remote Sensing Division, Washington, DC 20375, USA"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"given":"Steven P.","family":"Menk","sequence":"additional","affiliation":[{"name":"U.S. Naval Research Laboratory, Remote Sensing Division, Washington, DC 20375, USA"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"software","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-4906-730X","authenticated-orcid":false,"given":"Yanting","family":"Wang","sequence":"additional","affiliation":[{"name":"U.S. Naval Research Laboratory, Remote Sensing Division, Washington, DC 20375, USA"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Rodriguez-Morales, F., Paden, J., Mai, H., Occhiogrosso, V., Taylor, L., Talasila, H., Leuschen, C., Hale, R., Schroeder, B., and Kolli, J. (2024, January 7\u201312). A multi-channel UWB airborne microwave radar for swath mapping of snow layers. Proceedings of the IGARSS 2024\u20132024 IEEE International Geoscience and Remote Sensing Symposium, Athens, Greece.","DOI":"10.1109\/IGARSS53475.2024.10641248"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/TGRS.2021.3063756","article-title":"High-resolution snow depth on Arctic sea ice from low-altitude airborne microwave radar data","volume":"60","author":"Jutila","year":"2022","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"221","DOI":"10.1109\/TIM.2019.2893043","article-title":"Drone-mounted ultrawideband radar for retrieval of snowpack properties","volume":"69","author":"Jenssen","year":"2020","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/TGRS.2022.3223989","article-title":"Airborne UWB FMCW radar for snow depth measurements","volume":"60","author":"Kolpuke","year":"2022","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/LGRS.2021.3094165","article-title":"UAV-borne FMCW InSAR for focusing buried objects","volume":"19","author":"Burr","year":"2021","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"18","DOI":"10.1109\/74.755021","article-title":"Ultra-wide-band synthetic-aperture radar for mine-field detection","volume":"41","author":"Carin","year":"1999","journal-title":"IEEE Antennas Propag. Mag."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Taylor, J.D. (2000). The CARABAS II VHF synthetic aperture radar. Ultra-Wideband Radar Technology, CRC Press. Chapter 12.","DOI":"10.1201\/9781420037296.ch12"},{"key":"ref_8","first-page":"130","article-title":"P-3 ultrawideband SAR: System applications to foliage penetration","volume":"Volume 2757","author":"VandenBerg","year":"1996","journal-title":"Algorithms for Synthetic Aperture Radar Imagery III"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/TGRS.2025.3568267","article-title":"A multi-channel approach to ocean surface current measurement with an ultra-wideband ATI-SAR","volume":"63","author":"Sletten","year":"2025","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Kim, S., P\u00e9rez, V.M., Krieger, G., and Villano, M. (2024, January 7\u201312). Demonstration of frequency-dependent penetration depth estimation using SAR interferometry with wide fractional bandwidth. Proceedings of the IGARSS 2024\u20132024 IEEE International Geoscience and Remote Sensing Symposium, Athens, Greece.","DOI":"10.1109\/IGARSS53475.2024.10642476"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Kim, S., Krieger, G., and Villano, M. (2024). Volume structure retrieval using drone-based SAR interferometry with wide fractional bandwidth. Remote Sens., 16.","DOI":"10.3390\/rs16081352"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Siqueira, P., Tarres, M.C., Adam, M., Sutherland, E., Maloyan, J., Seaver, T., Tessier, R., Tsang, L., Borah, F., and Marshall, H.P. (2024, January 7\u201312). SNOWWI: A three-frequency InSAR for snow science applications. Proceedings of the IGARSS 2024\u20132024 IEEE International Geoscience and Remote Sensing Symposium, Athens, Greece.","DOI":"10.1109\/IGARSS53475.2024.10642002"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"897","DOI":"10.1109\/TAES.2020.3034030","article-title":"A new resonance phenomenon observed in UWB 14\u201350 GHz SAR and its application to the retrieval of thickness and dielectric properties of scene features","volume":"57","author":"Morrison","year":"2021","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"183","DOI":"10.1109\/JPROC.2025.3621586","article-title":"Spaceborne synthetic aperture radar: Future technologies and mission concepts","volume":"114","author":"Moreira","year":"2025","journal-title":"Proc. IEEE"},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Vehmas, R., Dogan, O., Ignatenko, V., Radius, A., Muff, D., Leprovost, P., Nottingham, M., Vilja, P., Seilonen, T., and Arbenina, M. (2024, January 7\u201312). A look at spotlight extended dwell\u2014A new level of information content from small-satellite SAR. Proceedings of the IGARSS 2024\u20132024 IEEE International Geoscience and Remote Sensing Symposium, Athens, Greece.","DOI":"10.1109\/IGARSS53475.2024.10640637"},{"key":"ref_16","unstructured":"Romeiser, R., and Graber, H.C. (2018, January 4\u20137). Advanced ocean wave retrieval from time series of spotlight SAR subaperture images. Proceedings of the EUSAR 2018; 12th European Conference on Synthetic Aperture Radar, Aachen, Germany."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1016\/j.heliyon.2024.e33208","article-title":"Hyperspectral imaging and its applications: A review","volume":"10","author":"Bhargava","year":"2024","journal-title":"Heliyon"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Jezek, K.C., Johnson, J.T., Tsang, L., Brogioni, M., Macelloni, G., Aksoy, M., Kaleschke, L., Wang, S., Leduc-Leballeur, M., and Yardim, C. (2022). A review of recent developments in low-frequency ultra-wideband microwave radiometry for studies of the cryosphere. Front. Earth Sci., 10.","DOI":"10.3389\/feart.2022.1029216"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"4894","DOI":"10.1109\/JSTARS.2021.3073286","article-title":"Microwave radiometry at frequencies from 500 to 1400 MHz: An emerging technology for Earth observations","volume":"14","author":"Johnson","year":"2021","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_20","unstructured":"Skolnik, M. (1980). Introduction to Radar Systems, McGraw-Hill. [2nd ed.]."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Cruz, H., V\u00e9stias, M., Monteiro, J., Neto, H., and Duarte, R.P. (2022). A review of synthetic-aperture radar image formation algorithms and implementations: A computational perspective. Remote Sens., 14.","DOI":"10.3390\/rs14051258"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1149","DOI":"10.1109\/36.193791","article-title":"The gridded trihedral: A new polarimetric SAR calibration reflector","volume":"30","author":"Sheen","year":"1992","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"440","DOI":"10.1109\/JSTARS.2020.3036392","article-title":"Performance of SAR polarimetric calibration using hybrid corner reflectors: Numerical simulations and experimental measurements","volume":"14","author":"Wang","year":"2020","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1109\/36.285192","article-title":"A unified algorithm for phase and cross-talk calibration of polarimetric data-theory and observations","volume":"32","author":"Quegan","year":"1994","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_25","unstructured":"Levis, C.A., Johnson, J.T., and Teixeira, F.L. (2010). Radiowave Propagation-Physics and Applications, John Wiley & Sons."},{"key":"ref_26","unstructured":"Jackson, J.D. (1999). Classical Electrodynamics, Wiley. [3rd ed.]."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"142","DOI":"10.1109\/JRPROC.1953.274171","article-title":"Toward a theory of reflection by a rough surface","volume":"41","author":"Ament","year":"1953","journal-title":"Proc. IRE"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1764","DOI":"10.1109\/TAES.2012.6178096","article-title":"On synthetic aperture radar azimuth and range resolution equations","volume":"48","author":"Vu","year":"2012","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_29","unstructured":"Balanis, C.A. (1989). Advanced Engineering Electromagnetics, Wiley."},{"key":"ref_30","unstructured":"Franceschetti, G., and Lanari, R. (1999). Synthetic Aperture Radar Processing, CRC Press."},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Stutzman, W.L., and Thiele, G.A. (1998). Antenna Theory and Design, Wiley.","DOI":"10.1002\/047134608X.W1206"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"401","DOI":"10.1109\/36.905248","article-title":"Dual-beam interferometry for ocean surface current vector mapping","volume":"39","author":"Frasier","year":"2001","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"4972","DOI":"10.1109\/TGRS.2017.2697843","article-title":"A Theoretical study of velocity SAR imaging of a moving, nonstationary scene","volume":"55","author":"Toporkov","year":"2017","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"396","DOI":"10.1109\/LGRS.2010.2078486","article-title":"Time-domain reconstruction algorithms for FMCW-SAR","volume":"8","author":"Ribalta","year":"2011","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Galati, G., Pavan, G., and Wasserzier, C. (2020). Characterization of back-scattering and multipath in a suburban area after the calibration of an X-Band commercial radar. Sensors, 20.","DOI":"10.3390\/s20020463"},{"key":"ref_36","unstructured":"Long, M.W. (2001). Radar Reflectivity of Land and Sea, Artech House."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"213","DOI":"10.1109\/36.285206","article-title":"Resolution of a phase ambiguity in a calibration procedure for polarimetric radar systems","volume":"32","author":"Sletten","year":"1994","journal-title":"IEEE Trans. Geosci. Remote Sens."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5737\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,9]],"date-time":"2026-09-09T15:02:42Z","timestamp":1788966162000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/18\/5737"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,9]]},"references-count":37,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["s26185737"],"URL":"https:\/\/doi.org\/10.3390\/s26185737","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,9]]}}}