{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:53:51Z","timestamp":1760237631296,"version":"build-2065373602"},"reference-count":9,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2020,6,1]],"date-time":"2020-06-01T00:00:00Z","timestamp":1590969600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Nowadays, stringent requirements for the quality of SAR data products exist. The radiometric and image quality requirements can only be fulfilled by knowing the disturbances caused by the radar hardware itself. The internal calibration is a mechanism to estimate these disturbances from the real hardware. Unfortunately, most of the current internal calibration schemes interrupt the SAR data acquisition during internal calibration and hence cause a loss of azimuth samples and a degradation of the image quality. The calibration is thus often performed only before and after a data take. However, these two calibration events are hardly sufficient to estimate the instrument parameters during the whole acquisition especially for long data takes, which will become more common in future SAR system. In this paper, an internal calibration scheme is introduced which allows performing the internal calibration during nominal data acquisition by injecting a coded calibration signal into the receiver with very low power. This signal causes only minor degradation of the SAR image but can be retrieved from the data using adequate signal processing. This technique is described, the theoretical performance estimated, and finally demonstrated on real data from the TerraSAR-X mission. A selection of possible coding scheme is also analyzed with respect to their suitability for the proposed internal calibration scheme.<\/jats:p>","DOI":"10.3390\/rs12111773","type":"journal-article","created":{"date-parts":[[2020,6,2]],"date-time":"2020-06-02T09:19:27Z","timestamp":1591089567000},"page":"1773","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Technique for Concurrent Internal Calibration during Data Acquisition for SAR Systems"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0650-9073","authenticated-orcid":false,"given":"Jens","family":"Reimann","sequence":"first","affiliation":[{"name":"Deutsches Zentrum f\u00fcr Luft- und Raumfahrt e.V., Institut f\u00fcr Hochfrequenztechnik und Radarsysteme, 82234 We\u00dfling, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0045-3726","authenticated-orcid":false,"given":"Marco","family":"Schwerdt","sequence":"additional","affiliation":[{"name":"Deutsches Zentrum f\u00fcr Luft- und Raumfahrt e.V., Institut f\u00fcr Hochfrequenztechnik und Radarsysteme, 82234 We\u00dfling, Germany"}]}],"member":"1968","published-online":{"date-parts":[[2020,6,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"753","DOI":"10.1109\/36.7707","article-title":"A Digital Calibration Method for Synthetic Aperture Radar Systems","volume":"26","author":"Larson","year":"1988","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_2","unstructured":"Dall, J., Skou, N., and Christensen, E.L. (1994, January 8\u201312). Pulse-Based Internal Calibration of Polarimetric SAR. Proceedings of the IGARSS \u201994\u20141994 IEEE International Geoscience and Remote Sensing Symposium, Pasadena, CA, USA."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1236","DOI":"10.1109\/TGRS.2008.2008719","article-title":"An Efficient Method for Performance Monitoring of Active Phased Array Antennas","volume":"47","author":"Schwerdt","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_4","unstructured":"Hounam, D., Schwerdt, M., and Zink, M. (2002, January 18\u201320). Active Antenna Module Characterisation by Pseudo-Noise Gating. Proceedings of the 25th ESA Antenna Workshop on Satellite Antenna Technology, Noordwijk, The Netherlands."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"727","DOI":"10.1109\/TGRS.2009.2035497","article-title":"TerraSAR-X SAR Processing and Products","volume":"48","author":"Breit","year":"2010","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Prats, P., Rodriguez-Cassola, M., Marotti, L., Naninni, M., Wollstadt, S., Schulze, D., Tous-Ramon, N., Younis, M., Krieger, G., and Reigber, A. (2010, January 25\u201330). Taxi: A versatile processing chain for experimental TanDEM-X product evaluation. Proceedings of the 2010 IEEE International Geoscience and Remote Sensing Symposium, Honolulu, HI, USA.","DOI":"10.1109\/IGARSS.2010.5651002"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"162","DOI":"10.1109\/TCOM.1964.1088973","article-title":"Dither Signals and Their Effect on Quantization Noise","volume":"12","author":"Schuchman","year":"1964","journal-title":"IEEE Trans. Commun. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"5","DOI":"10.2307\/2387224","article-title":"A Closed Set of Normal Orthogonal Functions","volume":"45","author":"Walsh","year":"1923","journal-title":"Am. J. Math."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"4462","DOI":"10.1109\/TGRS.2013.2282192","article-title":"Staggered SAR: High-Resolution Wide-Swath Imaging by Continuous PRI Variation","volume":"52","author":"Villano","year":"2014","journal-title":"IEEE Trans. Geosci. Remote Sens."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/11\/1773\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:34:30Z","timestamp":1760175270000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/12\/11\/1773"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,6,1]]},"references-count":9,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2020,6]]}},"alternative-id":["rs12111773"],"URL":"https:\/\/doi.org\/10.3390\/rs12111773","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2020,6,1]]}}}