Altimetry Measurements Research Articles

Mesoscale eddies off Peru in altimeter records: Identification algorithms and eddy spatio-temporal patterns

Relatively little is known about coherent vortices in the eastern South-Pacific along the Peruvian coast, even with regard to basic facts about their frequency of occurrence, longevity and structure. This study addresses these issues with nearly 15 years of relatively high-resolution satellite altimetry measurements. We first compare two distinct automated methods for eddy identification. The objective validation protocol shows that the rarely-used geometrical or “ winding-angle method”, based on the curvature of the streamline functions, is more accurate than the commonly-used “ Okubo–Weiss algorithm”, which defines a vortex as a simple connected region with values of Okubo–Weiss parameter weaker than a given threshold. We then investigate vortices off Peru using more than 20,000 mesoscale eddies identified by the winding-angle method. Coherent eddies, characterized by a high ratio of vorticity to deformation rate, are typically formed along the coast and propagate westward at 3–6 cm s −1. The vortices have a mean radius of 80 km, increasing northward, and are most frequently observed off of Chimbote (9°S) and south of San Juan (15°S). The mean eddy lifetime is about 1 month, but if eddies survive at least 2 months, the probability for surviving an additional week (or month) is constant at 90% (or 67%). Anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward. In general, cyclones and anticyclones are similar, except for eddies surviving at least 6 months. In this case, after a similar 3–4 months of radius and amplitude growth, amplitudes (or sizes) decay particularly rapidly for anticyclonic (or cyclonic) eddies. In terms of intensity, cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi-constant value, whereas anticyclones exhibit steady decline. Finally, eddy temporal variations were examined at seasonal and interannual scales in the “coastal” region favorable to the formation of energetic mesoscale structures. On seasonal scales, eddy activity is maximal in fall and minimum in spring. At interannual scales, the eddy activity index was maximal during the strong El Niño of 1997–1998 but another strong maximum of eddy activity also occurred late in 2004. These temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal-trapped waves which generate baroclinic instabilities. Further investigation of the mechanisms involved on the eddy genesis is needed.

Effects of mesoscale eddies on the flow of the Alaskan Stream

Using a high‐resolution, pan‐Arctic ice‐ocean model forced with realistic atmospheric data, we examine the mean transport and temporal and spatial variability within the Alaskan Stream. Model results are analyzed and compared with observations, including satellite altimetry and CTD measurements. The mean net transport of the Alaskan Stream is found to be between 34 and 44 Sv, intensifying downstream. Mesoscale eddies are found to periodically move along the path of the Alaskan Stream and alter the mean position of the typically westward‐flowing current. However, the strength of the current is not reduced as an anticyclonic eddy passes a point along the path. Instead, there appears to be an offshore (or southward) shift in the current velocity core. Stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy. This may result in recording of a weakened or sometimes reversed flow. Finally, we examine and demonstrate that modeled eddies within the Alaskan Stream have dominant effect on northward transport and variability through the eastern and central Aleutian Island passes.

A comparison of Greenland ice-sheet volume changes derived from altimetry measurements

AbstractWe compare rates of surface-elevation change on the Greenland ice sheet derived from European Remote-sensing Satellite-2 (ERS-2) radar-altimeter data with those obtained from laser-altimeter data collected over nearly the same time periods. Radar-altimeter data show more rapid thickening (9 ± 1 cm a−1 above 1500 m elevation in the north, and 3 ± 1 cm a−1 above 2000 m in the south) than the laser estimates, possibly caused by a lifting of the radar-reflection horizon associated with changes in the snowpack, such as those caused by progressively increased surface melting, as summer temperatures rise. Over all the ice sheet above 2000 m, this results in an ERS-derived volume balance ∼75 ± 15 km3 a−1 more positive than that from laser data. This bias between laser and radar estimates of elevation change varies spatially and temporally, so cannot at present be corrected without independent surveys such as those presented here. At lower elevations, comparison of detailed repeat laser surveys over Jakobshavn Isbræ with ERS results over the same time interval shows substantial ERS underestimation of ice-thinning rates. This results partly from missing data because of ‘bad’ radar waveforms over the very rough surface topography, and partly from the tendency for large radar footprints to sample preferentially local high points in the topography, thus missing regions of most rapid thinning along glacier depressions.

The GODAE/Mercator-Ocean global ocean forecasting system: results, applications and prospects

The Mercator-Océan eddy permitting (1/4) global ocean forecasting system assimilating satellite altimetry is the French contribution to the GODAE project and to the MERSEA project for operational systems. It has run operationally since October 2005 and is forced with daily surface fluxes from ECMWF operational analyses and forecasts. JASON, ERS and GFO altimetry measurements from AVISO were assimilated from January 2005 up to real time. The simulation results are compared with independent in-situ data of the Atlantic, Pacific and Antarctic Ocean basins in order to provide an estimation of the performance of the system. The results are also compared with the Levitus climatology, and with combinations of in-situ and satellite observations since 2005. In the Atlantic basin, the global system is also compared with Mercator-Ocean regional systems that assimilate SST (Sea Surface Temperature), SLA (Sea Level Anomalies) and in situ (temperature and salinity profiles) near real time observations

Comment on “On the steric and mass‐induced contributions to the annual sea level variations in the Mediterranean Sea” by David García et al.

[1] Garcia et al. [2006] (hereafter referred to as GCDVG) present an analysis of mass-induced sea level variation (SLVmass) of the Mediterranean Sea based on satellite altimetry, ocean modeling and Gravity Recovery and Climate Experiment (GRACE) gravity measurements. In particular, GCDVG find consistency between altimeter sea level variations corrected for steric effects and changes in oceanic mass derived from Gravity Recovery and Climate Experiment (GRACE). GCDVG show that the annual cycle of the sea level variability (SLVtotal) is dominated by changes in its steric part (SLVsteric) and that the basin average of mass (SLVmass) is maximum in February. They conclude that, when the sea level is rising (falling) the Mediterranean Sea is actually losing (gaining) mass. [2] GCDVG appear to use an unrealistically large estimate of steric sea level variability (SLVsteric) and neglect changes in continental water storage that can significantly affect GRACE measurements over the Mediterranean Sea. These issues are examined in turn below by reviewing relevant individual basin averages of the Mediterranean Sea in comparison to results of other studies. In particular, while also finding consistency between altimetry and GRACE measurements, Fenoglio-Marc et al. [2006] (hereafter referred to as FKB), in a similar study of the Mediterranean Sea, find steric effects only accounting for about 60% of the total annual sea level variability and the annual cycle of SLVmass having a maximum in November.

Combined airborne laser and radar altimeter measurements over the Fram Strait in May 2002

Knowledge of sea ice thickness is critical for the prediction of future climate, and for assessing the significance of changes in thickness. Sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard. However, a lack of knowledge of snow depth introduces significant uncertainties into these calculations. This paper compares the first coincident airborne laser and radar altimetry data over sea ice, collected during the Laser Radar Altimetry (LaRA) field campaign. LaRA was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard, and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth. Two new methods were created to analyse these data sets: a new radar retracker and a radar power simulator, which models radar returns from the laser data. We present the first quantitative analysis of data from the LaRA laser and radar altimeters, and demonstrate the potential of combining laser and radar altimetry to estimate snow depth. LaRA elevation estimates compare well with elevations from the radar altimeter onboard ERS-2 at the sub-meter level and the study provides lessons for future validation of satellite altimetry data over sea ice. Laser elevations are consistently higher than the radar elevations over snow covered sea ice. As LaRA was a flight of opportunity, no coincident in-situ measurements were available. Nevertheless, the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons.

Real-time kinematic tracking of towed AEM birds

In the absence of attitude and altitude sensors directly attached to the bird, helicopter airborne electromagnetic (AEM) data are typically interpreted assuming that the sensor bird maintains a fixed attitude as well as fixed vertical and horizontal offsets relative to the helicopter during survey. Laser altimeters fitted to the bird can be used for measuring bird-height over land, but these altimeters do not necessarily function over seawater, and in this case a fixed vertical offset is subtracted from the helicopter altimetry to estimate the height of the bird above sea level. With current navigation technology, these assumptions could be overcome by incorporating suitable altimetry and navigation sensors into AEM systems. We constructed an airborne testing rig to represent an AEM bird and fitted GPS, inertial navigation, and altimetry sensors to accurately measure bird attitude and height above seawater (as required for bathymetric mapping) during typical and atypical AEM-survey flight conditions. Bird height above sea level was measured with radar and laser altimeters, and was also estimated from the GPS receiver height. Bird attitude was obtained from the inertial navigation unit (INU) data and was compared with attitude data derived from a triangular configuration of three GPS antennas. Each antenna was linked to a pair of GPS receivers to allow comparison between dual-frequency, high-fidelity and single-frequency, low-fidelity measurements.Bird attitude and altimetry measurements were recorded during surveys flown offshore Tickera Bay (Spencer Gulf, SA) and within Broken Bay (Sydney, NSW). These surveys were flown at a maximum altitude of 180 m, with bird roll angles up to about ± 40°. Using dual-frequency GPS receivers, the agreement between heights derived from GPS and laser (radar) altimeter data is typically ~0.3 m (0.6 m). GPS antenna separations computed during flight from measured GPS positions gave agreement to within 0.4% (typically 0.2%) of measured values. The agreement between pitch and roll angles computed from GPS antenna positions and INU measurements was within ~1° and 2° respectively, neglecting the effects of any offsets in the alignment of coordinate axes between the two systems. A comparison of pitch and roll angles obtained from single and dual-frequency GPS receivers showed that the accuracy of pitch and roll angles obtained from single-frequency GPS receivers is generally about ± 2°. The discrepancy in results from the different GPS receivers increases at various points along the flight path. This increase was attributed to a decrease in accuracy in results from the single frequency GPS receivers. Roll and pitch angle profiles show oscillations consistent with harmonic (pendulum) motion of the bird at the end of the tow cable connecting the bird to the helicopter. We recommend the use of inertial navigation interfaced to a single dual-frequency GPS receiver for accurate attitude and position measurements, combined with laser and radar altimetry sensors. The future implications of this study are that we expect to accurately measure attitude and altitude of a towed bird over seawater and that consequently these altimetry and attitude sensors will be implemented on a new helicopter TEM system (SeaTEM) specifically designed for bathymetric mapping.

Improving the quality of satellite altimetry data over continental shelves

Satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean. Over continental shelves, however, the aliasing of unresolved high‐frequency signals of tidal and wind‐induced origin is the source of long‐wavelength errors that corrupt altimetry measurements and limit their use in shallow waters. In 2005, SSALTO/DUACS performed a complete reanalysis of altimeter data to accommodate the latest tidal model (GOT2000) and a correction for the aliased high‐frequency signals using a hydrodynamic model MOG2D‐G. This paper examines the quality and the performance of the newly released altimetry data over the northwest European shelf. This region is known for complex tides and for frequent storm surges. The newly corrected maps of sea level anomalies were compared with a previous altimetry product. Residual tidal aliasing was analyzed, and the impact of MOG2D‐G and GOT2000 models was assessed. Altimeter records were compared with tide gauge measurements. This research showed a significant reduction in the contamination of data by high‐frequency aliasing achieved through the use of the aforementioned models. However, aliased shallow‐water tidal constituents pose a serious problem, and it is obvious that future tidal corrections should feature local tides. Nonaliased, physical sea level variability was also studied focusing on interannual, seasonal, and intra‐annual (periods from 20 days to 1 year) modes. The magnitudes and the contributions of each mode to the total variance were estimated. It was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves.

Vertical Crustal Motion along the Mediterranean and Black Sea Coast Derived from Ocean Altimetry and Tide Gauge Data

Tide gauge (TG) data along the northern Mediterranean and Black Sea coasts are compared to the sea-surface height (SSH) anomaly obtained from ocean altimetry (TOPEX/Poseidon and ERS-1/2) for a period of nine years (1993–2001). The TG measures the SSH relative to the ground whereas the altimetry does so with respect to the geocentric reference frame; therefore their difference would be in principle a vertical ground motion of the TG sites, though there are different error sources for this estimate as is discussed in the paper. In this study we estimate such vertical ground motion, for each TG site, from the slope of the SSH time series of the (non-seasonal) difference between the TG record and the altimetry measurement at a point closest to the TG. Where possible, these estimates are further compared with those derived from nearby continuous Global Positioning System (GPS) data series. These results on vertical ground motion along the Mediterranean and Black Sea coasts provide useful source data for studying, contrasting, and constraining tectonic models of the region. For example, in the eastern coast of the Adriatic Sea and in the western coast of Greece, a general subsidence is observed which may be related to the Adriatic lithosphere subducting beneath the Eurasian plate along the Dinarides fault.

Airborne laser altimetry survey of Glaciar Tyndall, Patagonia

The first airborne laser altimetry measurements of a glacier in South America are presented. Data were collected in November of 2001 over Glaciar Tyndall, Torres del Paine National Park, Chilean Patagonia, onboard a Twin Otter airplane of the Chilean Air Force. A laser scanner with a rotating polygon-mirror system together with an Inertial Navigation System (INS) were fixed to the floor of the aircraft, and used in combination with two dual-frequency GPS receivers. Together, the laser–INS–GPS system had a nominal accuracy of 30 cm after data processing. On November 23rd, a total of 235 km were flown over the ablation area of Glaciar Tyndall, with 5 longitudinal tracks with a mean swath width of 300 m, which results in a point spacing of approximately 2 m both along and across track. A digital elevation model (DEM) generated using the laser altimetry data was compared with a DEM produced from a 1975 map (1:50,000 scale — Instituto Geográfico Militar (IGM), Chile). A mean thinning of − 3.1 ± 1.0 m a − 1 was calculated for the ablation area of Glaciar Tyndall, with a maximum value of − 7.7 ± 1.0 m a − 1 at the calving front at 50 m a.s.l. and minimum values of between − 1.0 and − 2.0 ± 1.0 m a − 1 at altitudes close to the equilibrium line altitude (900 m a.s.l.). The thinning rates derived from the airborne survey were similar to the results obtained by means of ground survey carried out at ∼ 600 m of altitude on Glaciar Tyndall between 1975 and 2002, yielding a mean thinning of − 3.2 m a − 1 [Raymond, C., Neumann, T.A., Rignot, E., Echelmeyer, K.A., Rivera, A., Casassa, G., 2005. Retreat of Tyndall Glacier, Patagonia, over the last half century. Journal of Glaciology 173 (51), 239–247.]. A good agreement was also found between ice elevation changes measured with laser data and previous results obtained with Shuttle Radar Topography Mission (SRTM) data. We conclude that airborne laser altimetry is an effective means for accurately detecting glacier elevation changes in Patagonia, where an ice thinning acceleration trend has been observed during recent years, presumably in response to warming and possibly also drier conditions.

Tsunami Source of the 2004 Sumatra–Andaman Earthquake Inferred from Tide Gauge and Satellite Data

Abstract Tsunami source of the 2004 Sumatra–Andaman earthquake was estimated from a joint inversion of tsunami waveforms recorded on tide gauges and sea surface heights captured by satellite altimetry measurements. The earthquake, the largest in the past 40 years, caused devastating tsunami damage to countries around the Indian Ocean, but the tsunami source, in particular, its northern end, was not well resolved. Although aftershocks and crustal deformation extended from off northwestern Sumatra Island through the Nicobar Islands to the Andaman Islands, some seismic-wave analyses indicated a shorter source length, several hundred kilometers. We used tsunami waveforms recorded at 12 tide gauge stations around the source and the sea surface heights measured by three satellites: Jason1, topex/Poseidon, and Envisat. We numerically computed tsunami propagation using realistic bathymetry; more than 66,000 depth points were digitized from nautical charts and combined with the ETOPO2 data. Inversion of satellite data indicates that the tsunami source extended to the Andaman Islands with a total length of 1,400 km, but such a model produces much larger tsunami waveforms than observed at Indian tide gauge stations. Inversion of tide gauge records and the joint inversion indicate that the tsunami source was about 900 km long. The largest slip, about 13 to 25 m, was located off Sumatra Island and the second largest slip, up to 7 m, near the Nicobar Islands. The slip distribution is similar for different rupture velocities and rise times, with a slow velocity of 1 km/sec and a rise time of 3 min yielding the largest variance reduction.

Present-day sea-level change: A review

Understanding of sea-level change has improved considerably over the last decade. Present-day knowledge of sea-level change is derived from tide gauge observations and satellite altimetry measurements. The average rate of sea-level change obtained from tide gauges over the last 50 years is + 1.8 ± 0.3 mm yr −1 . In comparison, altimeter measurements from TOPEX/Poseidon and Jason-1 have shown an average rise of + 3.1 ± 0.4 mm yr −1 since 1993. It is not clear yet whether the larger rate of rise of the last decade reflects acceleration or decadal fluctuation. The causes of the present-day rate are a combination of increases in ocean temperatures and land ice melt from mountain glaciers, Greenland, and Antarctica. Regional variability in sea-level change, as evidenced by the quasi global coverage of altimeter satellites, appears dominated by non uniform change of thermal expansion. New satellite technologies, such as InSAR, ICESat, and GRACE make significant contributions to understanding sea-level change. To cite this article: R.S. Nerem et al., C. R. Geoscience 338 (2006).

Updated estimates of glacier volume changes in the western Chugach Mountains, Alaska, and a comparison of regional extrapolation methods

We used airborne altimetry measurements to determine the volume changes of 23 glaciers in the western Chugach Mountains, Alaska, United States, between 1950/1957 and 2001/2004. Average net balance rates ranged between −3.1 to 0.16 m yr−1 for the tidewater and −1.5 to −0.02 m yr−1 for the nontidewater glaciers. We tested several methods for extrapolating these measurements to all the glaciers of the western Chugach Mountains using a process similar to cross validation. Predictions of individual glacier changes appear to be difficult, probably because of the effects of glacier dynamics, which on long (multidecadal) timescales, complicates the response of glaciers to climate. In contrast, estimates of regional contributions to rising sea level were similar for different methods, mainly because the large glaciers, whose changes dominated the regional total, were among those measured. For instance, the above sea level net balance rate of Columbia glacier (−3.1 ± 0.08 km3 yr−1 water equivalent (weq) or an equivalent rise in sea level (SLE) of 0.0090 ± 0.0002 mm yr−1) was nearly half of the total regional net balance rate of the western Chugach Mountain glaciers (−7.4 ± 1.1 km3 yr−1 weq or 0.020 ± 0.003 mm yr−1 SLE between 1950/1957 and 2001/2004). Columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate. Tidewater glaciers should therefore be treated separately when performing regional extrapolations.

A simulation of the OMEGA/Mars Express observations: Analysis of the atmospheric contribution

Spectral images of Mars obtained by the Mars Express/OMEGA experiment in the near infrared are the result of a complex combination of atmospheric, aerosol and ground features. Retrieving the atmospheric information from the data is important, not only to decorrelate mineralogical against atmospheric features, but also to retrieve the atmospheric variability. Once the illumination conditions have been taken into account, the main source of variation on the CO 2 absorption is due to the altitude of the surface, which governs atmospheric pressure variation by more than an order of magnitude between the summit of Olympus Mons down to the bottom of Valles Marineris. In this article we present a simplified atmospheric spectral model without scattering, specially developed for the OMEGA observations, which is used to retrieve the local topography through the analysis of the 2.0 μ m CO 2 band. OMEGA atmospheric observations increase the horizontal resolution compared to MOLA altimetry measurements, and therefore complement the mineralogical studies from the same instrument. Finally, residual variations of the pressure can be related to atmospheric structure variation.

Mars 1064 nm spectral radiance measurements determined from the receiver noise response of the Mars Orbiter Laser Altimeter

A technique was developed to compute the radiance of the scene viewed by the optical receiver of the Mars Orbiter Laser Altimeter. The technique used the detection threshold and the false detection rate of the receiver to provide a passive radiometry measurement of Mars at the 1064 nm wavelength over a 2 nm bandwidth and subkilometer spatial resolution in addition to the altimetry and active radiometry measurements. The passive radiometry measurement is shown to have a 2% or better precision and has been stable over several Martian years. We describe the principle of operation of the instrument and its calibration and assess its performance from sample orbital measurements.

The 2004 Indian Ocean tsunami: Tsunami source model from satellite altimetry

AbstractSatellite altimetry measurements of sea surface heights for the first-time captured the Indian Ocean tsunami generated from the December 2004 great Sumatra earthquake. Analysis of the sea surface height profile suggests that the tsunami source, or the seafloor deformation, of the great earthquake propagated to the north at an extremely slow speed of less than 1 km/sec on average for the entire 1300-km-long segment along the northern Sumatra-Nicobar-Andaman Trench. The extremely slow propagation speed produces a very long duration of tens minutes, longer than earthquake source duration estimated (480–500 sec) from short-periodP-wave radiation. The satellite altimetry data requires a total seismic moment of 9.86 × 1022Nm (Mw=9.3). This estimate is approximately 2.5 times larger than the value from long-period surface wave analysis but nearly the same as that from the ultra-long-period normal mode study. The maximum amount of slip (∼30 m) is identified in an offshore region closest to the northern most part of Sumatra where the largest tsunami run-up heights were observed.

Snowfall-Driven Growth in East Antarctic Ice Sheet Mitigates Recent Sea-Level Rise

Satellite radar altimetry measurements indicate that the East Antarctic ice-sheet interior north of 81.6 degrees S increased in mass by 45 +/- 7 billion metric tons per year from 1992 to 2003. Comparisons with contemporaneous meteorological model snowfall estimates suggest that the gain in mass was associated with increased precipitation. A gain of this magnitude is enough to slow sea-level rise by 0.12 +/- 0.02 millimeters per year.

Eddy-Induced Heat Transport in the Subtropical North Pacific from Argo, TMI, and Altimetry Measurements

Abstract Basin-scale heat transport induced by mesoscale oceanic eddies is estimated by combining satellite-derived sea surface height and temperature [temperature data are from the TRMM Microwave Imager (TMI)] data with Argo float temperature–salinity data. In the North Pacific Ocean subtropical gyre, warm (cold) temperature anomalies of mesoscale eddies are found to be consistently located to the west of high (low) SSH anomalies. The phase misalignment between the temperature and velocity anomalies, however, is largely confined to the seasonal thermocline, causing most of the eddy-induced heat transport to be carried in the surface 200-m layer. By establishing a statistical relationship between the surface and depth-integrated values of the eddy heat transport, the basin-scale eddy heat transport is derived from the concurrent satellite SSH/SST data of the past six years. In the Kuroshio Extension region, the meandering zonal jet is found to generate oppositely signed eddy heat fluxes. As a result, the zonally integrated poleward heat transport associated with the Kuroshio Extension is at a level O(0.1 PW), smaller than the previous estimates based on turbulent closure schemes. Large poleward eddy heat transport is also found in the subtropical North Pacific along a southwest–northeast-tilting band between Taiwan and the Midway Islands. This band corresponds to the region of the subtropical front, and it is argued that the relevant temperature field for identifying this band in the turbulent closure scheme models should be that averaged over the seasonal thermocline.

Interpretation of the anomalous growth of Austfonna, Svalbard, a large Arctic ice cap

AbstractAs previously reported, repeat-pass airborne laser altimetry measurements made in May 1996 and May 2002 show a large positive ice-surface elevation change rate over parts of the accumulation area of Austfonna, eastern Svalbard. The maximum growth rate is estimated to be equivalent to a 35–40% increase in snowfall over the area of thickening. Thinning is observed at lower elevations. Here we discuss in detail the possible causes of these elevation changes, including ice-cap dynamics and/or firn density changes, and conclude that sea-ice loss producing a localized increase in precipitation over Austfonna remains the most convincing explanation. This study highlights the problems of interpreting relatively short-term altimetry measurements where auxiliary data are limited in both spatial and temporal extent.

Digital elevation model construction from structured topographic data: The DEST algorithm

An algorithm, Determination of Earth Surface Structures (DEST), is presented to reconstruct digital terrain models of complex landforms from topographic data, such as contour lines and spot heights. The algorithm provides a triangular irregular network (TIN) of the source data, based on a modified Delaunay approach. Delaunay triangulation can introduce artificial terraces from a nonrandom distribution of input points such as a sampled contour line. The algorithm proposed here constructs the three‐dimensional principal skeletons of these artificial flat areas, eliminating the unwanted effects of contour lines. The algorithm can also be applied to topographic data from a variety of mixed sources such as photogrammetric information, radar altimetry measurements, and traditional contour lines. The sparse fine‐surface structures present in the source data are preserved, allowing accurate morphological evaluations, tectonic lineament extraction, and volume estimation. A methodology (D‐DEST) to easily derive, from a TIN computed by DEST, the drainage path and the catchment areas is also presented. A comparison of DEST with other methodologies is performed. It results that our approach does not introduce sensible biased effects in slopes, aspects, drainage network, and catchment areas. The evolution of the upper cone of Vesuvius volcano (Italy) during the last century, as derived from historical cartography, is presented as an application of DEST. The algorithm implemented in C can be requested at DEST_pareschi@pi.ingv.it.