{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T08:11:44Z","timestamp":1776931904147,"version":"3.51.2"},"reference-count":54,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2019,7,29]],"date-time":"2019-07-29T00:00:00Z","timestamp":1564358400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We present a new solution for the phase-preserving focusing of synthetic aperture radar (SAR) raw data acquired through the Terrain Observation with Progressive Scan (TOPS) mode. The proposed algorithm consists of a first interpolation stage of the TOPS raw data, which takes into account the Doppler Centroid frequency variations due to the azimuth antenna steering function, and allows us to unfold the azimuth spectra of the TOPS raw data. Subsequently, the interpolated signals are processed by using conventional phase-preserving SAR focusing methods that exploit frequency domain and spectral analyses algorithms, which are extensively used to efficiently process Stripmap and ScanSAR data. Accordingly, the developed focusing approach is easy to implement. In particular, the presented focusing approach exploits one of the available frequency domain Stripmap processing techniques. The only modification is represented by the inclusion, within the 2D frequency domain focusing step, of a spurious azimuth chirp signal with a properly selected azimuthal rate. This allows us to efficiently carry out the TOPS azimuth focusing through the SPECAN method. Furthermore, an important aspect of this algorithm is the possibility to easily achieve a constant and tunable output azimuth pixel size without any additional computing time; this is a remarkable feature with respect to the full-aperture TOPS-mode algorithms available in the existing literature. Moreover, although tailored on Sentinel-1 (S1) raw data, the proposed algorithm can be easily extended to process data collected through the TOPS mode by different radar sensors. The presented experimental results have been obtained by processing real Sentinel-1 raw data and confirm the effectiveness of the proposed algorithm.<\/jats:p>","DOI":"10.3390\/s19153321","type":"journal-article","created":{"date-parts":[[2019,7,29]],"date-time":"2019-07-29T03:06:58Z","timestamp":1564369618000},"page":"3321","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["A Phase-Preserving Focusing Technique for TOPS Mode SAR Raw Data Based on Conventional Processing Methods"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7847-7576","authenticated-orcid":false,"given":"Adele","family":"Fusco","sequence":"first","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7843-3565","authenticated-orcid":false,"given":"Antonio","family":"Pepe","sequence":"additional","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Paolo","family":"Berardino","sequence":"additional","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5197-7503","authenticated-orcid":false,"given":"Claudio","family":"De Luca","sequence":"additional","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sabatino","family":"Buonanno","sequence":"additional","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7296-2749","authenticated-orcid":false,"given":"Riccardo","family":"Lanari","sequence":"additional","affiliation":[{"name":"IREA\u2014National Research Council of Italy (CNR) via Diocleziano 328, 80124 Napoli, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,7,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1109\/MGRS.2013.2248301","article-title":"A tutorial on synthetic aperture radar","volume":"1","author":"Moreira","year":"2013","journal-title":"IEEE Geosci. Remote Sens. Mag."},{"key":"ref_2","unstructured":"Curlander, J.C., and McDonough, R.N. (1991). Synthetic Aperture Radar\u2014Systems And Signal Processing, John Wiley & Sons, Inc."},{"key":"ref_3","unstructured":"Franceschetti, G., and Lanari, R. (1999). Synthetic Aperture Radar Processing, Electronic Engineering Systems, Taylor & Francis."},{"key":"ref_4","unstructured":"Cumming, I., and Wong, F. (2005). Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation, Number v. 1 in Artech House remote sensing library, Artech House."},{"key":"ref_5","unstructured":"Carrara, W., Goodman, R., and Majewski, R. (1995). Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, Artech House signal processing library, Artech House."},{"key":"ref_6","first-page":"366","article-title":"High resolution processing of hybrid strip-map\/spotlight mode SAR","volume":"143","author":"Baker","year":"1996","journal-title":"IET J. Mag."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2352","DOI":"10.1109\/TGRS.2006.873853","article-title":"TOPSAR: Terrain Observation by Progressive Scans","volume":"44","author":"Guarnieri","year":"2006","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1016\/j.rse.2011.05.028","article-title":"GMES Sentinel-1 mission","volume":"120","author":"Torres","year":"2012","journal-title":"Remote Sens. Environ."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Geudtner, D., Torres, R., Snoeij, P., Davidson, M., and Rommen, B. (2014, January 13\u201318). Sentinel-1 System capabilities and applications. Proceedings of the 2014 IEEE Geoscience and Remote Sensing Symposium, Quebec City, QC, Canada.","DOI":"10.1109\/IGARSS.2014.6946711"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Janoth, J., Gantert, S., Schrage, T., and Kaptein, A. (2013, January 21\u201326). Terrasar next generation\u2014Mission capabilities. Proceedings of the 2013 IEEE International Geoscience and Remote Sensing Symposium\u2014 IGARSS, Melbourne, VIC, Australia.","DOI":"10.1109\/IGARSS.2013.6723277"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"19","DOI":"10.2528\/PIER11030209","article-title":"MIMO-TOPS mode for high-resolution ultra-wide-swath full polarimetric imaging","volume":"121","author":"Xu","year":"2011","journal-title":"Progress Electromagn. Res."},{"key":"ref_12","unstructured":"Deng, Y., and Huang, M. (2010, January 7\u201310). Tri-band Multi-Polarity Airborne SAR System. Proceedings of the 8th European Conference on Synthetic Aperture Radar, Aachen, Germany."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"108","DOI":"10.1109\/TGRS.1981.350361","article-title":"Conceptual Performance of a Satellite Borne, Wide Swath Synthetic Aperture Radar","volume":"GE-19","author":"Tomiyasu","year":"1981","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"722","DOI":"10.1109\/36.387587","article-title":"Optimum look weighting for burst-mode and ScanSAR processing","volume":"33","author":"Bamler","year":"1995","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3933","DOI":"10.1109\/TGRS.2009.2027596","article-title":"A New Method for Correcting ScanSAR Scalloping Using Forests and Inter-SCAN Banding Employing Dynamic Filtering","volume":"47","author":"Shimada","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Romeiser, R., Horstmann, J., and Graber, H. (2010, January 25\u201330). A new scalloping filter algorithm for scansar images. Proceedings of the 2010 IEEE International Geoscience and Remote Sensing Symposium, Honolulu, HI, USA.","DOI":"10.1109\/IGARSS.2010.5652039"},{"key":"ref_17","unstructured":"Cumming, I., and Bennett, J. (1979, January 2\u20134). Digital processing of Seasat SAR data. Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP\u201979), Washington, DC, USA."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"706","DOI":"10.1109\/36.158864","article-title":"A comparison of range-Doppler and wavenumber domain SAR focusing algorithms","volume":"30","author":"Bamler","year":"1992","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"786","DOI":"10.1109\/36.298008","article-title":"Precision SAR processing using chirp scaling","volume":"32","author":"Raney","year":"1994","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_20","unstructured":"Hughes, W., Gault, K., and Princz, G.J. (1996, January 31\u201331). A comparison of the Range-Doppler and Chirp Scaling algorithms with reference to RADARSAT. Proceedings of the 1996 International Geoscience and Remote Sensing Symposium (IGARSS\u201996), Lincoln, NE, USA."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1123","DOI":"10.1109\/36.536528","article-title":"Extended chirp scaling algorithm for air- and spaceborne SAR data processing in stripmap and ScanSAR imaging modes","volume":"34","author":"Moreira","year":"1996","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"809","DOI":"10.1111\/j.1365-2478.1989.tb02235.x","article-title":"Synthetic Aperture Radar for wave application techniques","volume":"37","author":"Rocca","year":"1989","journal-title":"Geophys. Prospect."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"194","DOI":"10.1109\/7.78293","article-title":"SAR data focusing using seismic migration techniques","volume":"27","author":"Cafforio","year":"1991","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"356","DOI":"10.1109\/7.53462","article-title":"A SAR processor based on two-dimensional FFT codes","volume":"26","author":"Franceschetti","year":"1990","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"107","DOI":"10.1049\/ip-f-2.1992.0014","article-title":"WASAR: a wide-angle SAR processor","volume":"139","author":"Franceschetti","year":"1992","journal-title":"IEE Proc. F Radar Signal Process."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"227","DOI":"10.1109\/7.366305","article-title":"Efficient and high precision space-variant processing of SAR data","volume":"31","author":"Franceschetti","year":"1995","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"854","DOI":"10.1109\/7.489529","article-title":"A new two-dimensional squint mode SAR processor","volume":"32","author":"Franceschetti","year":"1996","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1296","DOI":"10.1109\/36.469496","article-title":"A new method for the compensation of the SAR range cell migration based on the chirp z-transform","volume":"33","author":"Lanari","year":"1995","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1446","DOI":"10.1109\/36.649799","article-title":"A short discussion on the exact compensation of the SAR range-dependent range cell migration effect","volume":"35","author":"Lanari","year":"1997","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_30","unstructured":"Mittermayer, J., Lord, R., and Borner, E. (2003, January 21\u201325). Sliding spotlight SAR processing for TerraSAR-X using a new formulation of the extended chirp scaling algorithm. Proceedings of the 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477), Toulouse, France."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"770","DOI":"10.1109\/TGRS.2009.2027701","article-title":"Processing of Sliding Spotlight and TOPS SAR Data Using Baseband Azimuth Scaling","volume":"48","author":"Prats","year":"2010","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"270","DOI":"10.1016\/j.asr.2011.03.024","article-title":"TOPSAR data focusing based on azimuth scaling preprocessing","volume":"48","author":"Xu","year":"2011","journal-title":"Adv. Space Res."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"297","DOI":"10.2528\/PIERB12081804","article-title":"An efficient imaging approach for TOPS SAR data focusing based on scaled fourier transform","volume":"47","author":"Huang","year":"2013","journal-title":"Progress Electromagn. Res."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1036","DOI":"10.1109\/LGRS.2011.2151174","article-title":"Sliding Spotlight and TOPS SAR Data Processing Without Subaperture","volume":"8","author":"Sun","year":"2011","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"929","DOI":"10.1109\/LGRS.2011.2135837","article-title":"An Efficient Approach With Scaling Factors for TOPS-Mode SAR Data Focusing","volume":"8","author":"Xu","year":"2011","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1109\/JSTARS.2013.2260134","article-title":"TOPS-Mode Raw Data Processing Using Chirp Scaling Algorithm","volume":"7","author":"Xu","year":"2014","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Yang, W., Chen, J., Zeng, H.C., Wang, P.B., and Liu, W. (2016). A Wide-Swath Spaceborne TOPS SAR Image Formation Algorithm Based on Chirp Scaling and Chirp-Z Transform. Sensors, 16.","DOI":"10.3390\/s16122095"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"6910","DOI":"10.1109\/TGRS.2017.2735993","article-title":"A Modified Three-Step Algorithm for TOPS and Sliding Spotlight SAR Data Processing","volume":"55","author":"Yang","year":"2017","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"3688","DOI":"10.1109\/TGRS.2011.2145384","article-title":"Efficient Full Aperture Processing of TOPS Mode Data Using the Moving Band Chirp Z-Transform","volume":"49","author":"Engen","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1029\/97RG03139","article-title":"Radar interferometry and its application to changes in the Earth\u2019s surface","volume":"36","author":"Massonnet","year":"1998","journal-title":"Rev. Geophys."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"333","DOI":"10.1109\/5.838084","article-title":"Synthetic aperture radar interferometry","volume":"88","author":"Rosen","year":"2000","journal-title":"Proc. IEEE"},{"key":"ref_42","unstructured":"Bamler, R., and Sch\u00e4ttler, B. (1995). Phase-Preservation in SAR Processing: Definition, Requirements and Tests, DLR Publisher. DLR Tech, Note Ver 1.0."},{"key":"ref_43","unstructured":"ESA (2019). RADAR and SAR Glossary, Available online: https:\/\/earth.esa.int\/handbooks\/asar\/CNTR5-2.html."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"45","DOI":"10.1049\/ip-f-1.1985.0006","article-title":"Application of efficient linear FM matched filtering algorithms to synthetic aperture radar processing","volume":"132","author":"Sack","year":"1985","journal-title":"IEE Proc. F (Commun. Radar Signal Process.)"},{"key":"ref_45","unstructured":"Piantanida, R., Hajduch, G., and Poullaouec, J. (2017). Sentinel-1 Level 1 Detailed Algorithm Definition, MDA. Technical Report."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"297","DOI":"10.1090\/S0025-5718-1965-0178586-1","article-title":"An algorithm for the machine calculation of complex Fourier series","volume":"19","author":"Cooley","year":"1965","journal-title":"Math. Comput."},{"key":"ref_47","unstructured":"Lyons, R.G. (2004). Understanding Digital Signal Processing, Prentice Hall PTR. [2nd ed.]."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1190\/1.1440826","article-title":"Migration by Fourier Transform","volume":"43","author":"Stolt","year":"1978","journal-title":"Geophysics"},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"254","DOI":"10.1049\/ip-rsn:19982218","article-title":"Chirp z-transform based SPECAN approach for phase-preserving ScanSAR image generation","volume":"145","author":"Lanari","year":"1998","journal-title":"IEE Proc. -Radar Sonar Navig."},{"key":"ref_50","doi-asserted-by":"crossref","unstructured":"Reimann, J., Schwerdt, M., Schmidt, K., Ramon, N.T., Castellanos, G.A., D\u00f6ring, B., Rudolf, D., Raab, S., Antony, J.M.W., and Zink, M. (2015, January 1\u20134). The DLR SAR calibration center. Proceedings of the 2015 IEEE 5th Asia-Pacific Conference on Synthetic Aperture Radar (APSAR), Singapore.","DOI":"10.1109\/APSAR.2015.7306181"},{"key":"ref_51","unstructured":"(2019). ESA. Copernicus Open Access Hub, Available online: https:\/\/scihub.copernicus.eu\/."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1109\/MSP.2009.935383","article-title":"Synthetic Aperture Radar Processing with GPGPU","volume":"27","author":"Galdi","year":"2010","journal-title":"IEEE Signal Process. Mag."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"4712","DOI":"10.1109\/TGRS.2016.2550201","article-title":"Spaceborne Synthetic Aperture Radar Data Focusing on Multicore-Based Architectures","volume":"54","author":"Imperatore","year":"2016","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_54","unstructured":"Kirk, D.B., and Hwu, W.M.W. (2010). Programming Massively Parallel Processors: A Hands-on Approach, Morgan Kaufmann Publishers Inc.. [1st ed.]."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/15\/3321\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T13:10:42Z","timestamp":1760188242000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/15\/3321"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,7,29]]},"references-count":54,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2019,8]]}},"alternative-id":["s19153321"],"URL":"https:\/\/doi.org\/10.3390\/s19153321","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,7,29]]}}}