## 1 Introduction  
Though initially conceived for performing ocean topography measurements [1, 2], radar altimeters promptly demonstrated their utility in other fields such as sea ice [3], land ice [4], and inland water level (WL) monitoring [5, 6, 7]. As of today, classic radar altimeter processing techniques, namely Low-Resolution Mode (LRM) and UnFocused Synthetic Aperture Radar (UFSAR), are used by the operational processors of most radar altimeters, such as CryoSat-2 (CS2), Sentinel-3 A/B (S3A, S3B), and Sentinel-6 Michael Freilich (S6). These techniques are limited in terms of along-track resolution to a range of about a few kilometers depending on the topography for LRM, and to about 300 m for UFSAR [8, 9]. Such along-track resolution is sufficient for many applications over vast distributed scenarios, including Global Mean Sea Level monitoring [10] and studies of weather mechanisms [11], but it does limit radar altimetry capabilities in other applications, such as hydrology, where targets of interest can be narrower than 100 m.  
In order to avoid confusion, in the present study we have named WL\({}_{i}\) the water level obtained from a single radar waveform, WL\({}_{a}\) the statistical aggregation of all the WL\({}_{i}\)s measured in a single satellite pass over the water body of interest, and WL\({}_{t}\) the true water level of the targeted water body or the one measured by the corresponding hydrological station. In the discussion surrounding the error of methods in the retrieval of inland WL\({}_{a}\)s, a frequently reported parameter is the water extension of the target. Although the extension influences the physical behavior of the water and, thus, the shape of the waveforms of radar pulses, it can be misleading since it is not directly related to the number of measurements. In contrast, transect length provides a more accurate description as it directly determines the expected number of measurements available for statistical analysis. It is widely accepted to categorize the targets according to the length of the transect with respect to the altimeter's along-track resolution [12]: if the length is below the along-track resolution, it is considered small; if it is in the same order of magnitude, we consider it medium; and if it is larger by more than one order of magnitude, we consider it large. It is important to underline that some targets, such as Victoria Lake, are so large that from the perspective of the altimeter's footprint, the shape of the waveforms resembles the one obtained over the ocean. In this article, we use the along-track resolution from UFSAR (300 m) as a reference to classify the size of the targets, as it is the current operational algorithm of S6. Over the ocean, waveforms from radar pulses transmitted by altimeters are well understood, and thus can be physically modeled and analyzed using specific ocean retrackers based on the waveform model, such as the one developed by [PERSON] et al. [13], which leads to sea level estimation errors below 20 cm [9; 14]. Unfortunately, when the altimeter is measuring over coastal or inland waters, changes in the physical dynamics of water, the presence of untargeted bright scatterers, and the complexity of the terrain within the altimeter's footprint can contaminate the waveforms, resulting in unpredictable shapes. As a consequence, great effort has been invested in developing robust retrackers that can handle waveform contamination, such as the Offset Center of Gravity retracker (OCOG) [15], and retrackers specifically tailored to coastal and inland waters [16; 17; 18; 19; 20]. Studies about performance over large lakes have previously reported WL\({}_{a}\) estimations with an error below 10 cm [17; 21; 22; 23; 24; 25]. In these studies, there are usually three main topics: (1) which satellite measurements are assigned to the target, (2) which retracker is used, and (3) the method used for filtering WL\({}_{a}\)s. In practice, as the algorithms to obtain the WL\({}_{a}\) estimation become more complex, these topics can become interdependent.