The observation of ocean scales smaller than 100 km with low-resolution mode (LRM) altimetry products is degraded by the existence of a ''hump artifact'' visible on sea surface height (SSH) spectra.Through an analysis of simulations and actual data from multiple missions, this paper shows that the hump originates in a response to inhomogeneities in backscatter strength. Current retrackers cannot fit their Brown model properly because they were designed for a scene with homogeneous backscatter properties. The error is also smoothed along track because of the size and shape of the LRM disc-shaped footprint. Therefore, the hump is modulated by the altimeter design and altitude and by the retracker used.Because of the random nature of the phenomenon, a large majority of long topography segments (e.g., hundreds to thousands of kilometers) is affected. However, within these segments, a substantial fraction of the corruption is contained in small subsets of data (e.g., less than 10%). This paper shows that oceanography users interested in small-scale SSH signals can mitigate the hump corruption by using better editing and postprocessing algorithms on the 20-Hz rate of current products.Last, the thin stripe-shaped footprint of Cryosat-2's synthetic aperture radar mode (SARM) is not affected by the hump artifact, thus improving the observation of topography features ranging from 30 to 100 km. The differences between SARM and pseudo-LRM sigma0 can also be used to detect major hump events on pseudo-LRM data, which might be an asset to design/validate a new generation of algorithms aimed at reducing the hump artifact on the existing LRM record.

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This study presents a new method of precise altimeter absolute calibration using a dedicated microwave transponder, which acts as an altimeter signal repeater that can be deployed at any sub-track position both in coastal regions and inland. The Austrian Academy of Sciences operates an altimeter transponder at the Gavdos calibration/validation facility located beneath a Jason cross-over point.We discuss the capabilities and strengths of the transponder technique in general and in the particular case of a dedicated calibration campaign carried out in 2011. For the accomplishment of this campaign, including 26 ascending and descending Jason-2 passes, the onboard Poseidon-3 altimeter had to be switched to the DIODE/DEM mode for every overflight. Four different methods have been developed to analyze the transponder generated waveforms, provided by S-IGDR and S-GDR products, respectively.The resulting biases of the altimetric ranges have proven to be stable (3 mm rms) and agree to a large extent among the proposed algorithms. However, the absolute bias value of 25.8 ± 0.3 cm derived from the transponder calibration technique shows a significant deviation of several centimeters compared with the ones resulting from conventional techniques. Possible causes of this behavior are under further investigation.

Jason-2 was successfully launched by a Boeing Delta II rocket from the Vandenberg site, California. The OSTM/Jason-2 project is a cooperation among NASA, NOAA, EUMETSAT, and CNES. The first two months of the OSTM/Jason-2 mission have been dedicated to the assessment of the overall system. The goal of this assessment phase was:(i) to assess the behavior of the spacecraft, at the platform and payload levels; (ii) to verify that platform performance requirements are met with respect to Jason-2 requirements; (iii) to verify that payload instruments performance requirements evaluated at instrument level are met; and (iv) to assess the performance of the Jason-2 Ground System. The paper will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications.

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