2018/1/3 Radar altimetry backscattering signatures at Ka, Ku, C and S bands over the ocean Blarel F.*a, Frappart F.a,b; Blumstein D.a,c, Birol F. a, Morrow R. a, Nino F. a (a)- Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS-GRGS), UMR 5566, CNES/CNRS/IRD/UPS, Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, 31400 Toulouse, France, (b)- Géosciences Environnement Toulouse (GET-GRGS), UMR 5563, CNRS/IRD/UPS, Observatoire Midi-Pyrénées, 14 Avenue Edouard Belin, 31400 Toulouse, France, (c)- Centre National d’Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France, ENVISAT.v21 Ku band (13.575 GHz) S band (3.2 GHz) JASON 2 : Backscatter difference C-Ku band 1 Introduction ENVISAT v2.1 : Backscatter difference S-Ku band In this study, we present global maps of along-track average backscattering coefficients (from Ice-1 [1] and Ice-2 [2] retracker) and associated standard deviation at : Ku band using ERS-2, ENVISAT, and Jason-2 (Ice-1 only) data S band using ENVISAT data C band using Jason-2 (Ice-1 only) data Ka band using SARAL data for land. The resulting maps have been obtained from a original method developed to compute any statistics along the pass. JASON 1 Ku band (13.575 GHz) C band (5.4 GHz) Datasets ERS-2: The data product CTOH release [3-4-5]. Its data are available from May 1995 to June 2003 (cycle 1 to 85). ENVISAT v2.1 : The data product REAPER release [6]. Its orbit characteristics are the same as for ERS-2. Its data are available from May 2002 to October 2010 (cycle 6 to 94). SARAL: The data product CNES release [7]. Placed in the same orbit as the ENVISAT satellite. Its data are available from March 2013 to August 2015 (cycle 1 to 25). JASON-2 mission: Its orbit is different of the above missions. Its data used are from August 2008 to February 2016 (cycle 0 to 279). JASON 2 Ku band (13.575 GHz) C band (5.4 GHz) Backscatter overs ocean Mean pass Method Mean altimetry pass (black arrow)obtained as the average of all altimetry data acquired during the life time of an altimetry mission. Altimetry measurements are epresented using dots, each color representing a cycle. Rectangles represent the cells along the altimetry pass defined by δAlong-track and δCross-track for a given location (λcell, φcell) (yellow and black star) Along-track altimetry data were first sorted using a normalized pass [8] in order to merge the data measurements into cells regularly organized along the pathway. The mean pass is then defined by four parameters: the mean longitude and latitude of each cell composing the mean pass, and its size given by its dimensions along (δAlong-track) and cross track (δCross-track). If δCross-track is chosen arbitrarily (equals two kilometers in this study as this distance corresponds to the maximum cross-track variations along the orbit of ERS-2, ENVISAT, SARAL and Jason-2 missions), δAlong-track is given by : δAlong-track = Vsat δt where Vsat is the velocity of the satellite along the orbit equals to 7.45 km.s-1 and δt is chosen equals to 1 second, that mean that every cell contains, each cycle a maximum of 20 measurements. (λcell, φcell) Conclusion & Results Cell along average track. References Altimetry data in one cell for several cycles [1]- Wingham et al, Sepember 1986, Proceedings of the IGARSS Symposium: New techniques in satellite altimeter tracking systems, Zurich, Switzerland [2]- Legresy et al, 2005, Remote Sensing of Environment 95, nᵒ 2, doi:10.1016/j.rse.2004.11.018. [3]- Frappart et al. 2016. « An ERS-2 altimetry product compatible with ENVISAT for continental and ice surface studies. ». Remote Sensing of Environment. [4]- Blarel et al., 2015, “Altimetric backscattering signatures at Ka, Ku and S bands over global land surfaces”, SPIE, Toulouse, France [5]- CTOH. 2015.http://ctoh.legos.obs-mip.fr/products/alongtrack-data/ctoh-ers-2-handbook [6]-ESA.2011.https://earth.esa.int/documents/10174/1912962/ra2-mwr.ProductHandbook.2_2.pdf [7]- CNES. 2013.http://www.aviso.altimetry.fr/fileadmin/documents/data/tools/SARAL_Altika_products_handbook.pdf [8]- Blarel et al. 2015. CTOH Technical report: ”Normalized Altimetric Pass”. http://ctoh.legos.obs-mip.fr δAzimuth=Vsat*δt δCross-track Backscatter difference ESA, Living Planet Symposium, May 2016, Prague, Czech Republic