Coseismic lateral offsets of surface rupture zone produced by the 2001 Mw 7.8 Kunlun earthquake,Tibet from the IKONOS and QuickBird imagery

Analyses and interpretations of 1m‐resolution IKONOS, and 61cm‐resolution QuickBird images reveal that the distribution of strike‐slip offsets and ground deformation characteristics of the coseismic surface rupture produced by the 2001 M _w 7.8 Kunlun earthquake occurred in the western segment of the strike‐slip Kunlun fault, northern Tibet. The 2001 coseismic strike‐slip offsets measured from IKONOS images range from 2 m up to 16.7 m, generally 3–8 m, which are generally consistent with those measured immediately in the field after the earthquake. The coseismic surface ruptures along which offsets were observed are mainly composed of a numerous of en echelon shear faults and cracks which are concentrated on a rupture zone ranging from a few meters up to ～500 m in width. The offsets measured along individual shear faults or crack are typically 2–7 m, but up to >10 m in several locations. Our results show that high resolution remote sensing imagery provides a powerful tool for measuring coseismic strike‐slip offsets and detecting the ground deformation produced by a large earthquake in the remote and high mountain Tibet region.     

Uplift and subsidence due to the 26 December 2004 Indonesian earthquake detected by SAR data

The Indonesian earthquake took place on 26 December 2004 at 00:58 GMT (moment magnitude 9.3) in the Indian Ocean, offshore the west coast of Sumatra, at a depth of about 30 km. This earthquake is one of the largest of the past 100 years, comparable only with those in Chile (1960) and Alaska (1964). The earthquake originated in the subduction zone of the Indian and Burma plates, moving at a relative velocity of 6 cm/year. The aftershocks were distributed along a plate boundary of about 1000–1300 km between Sumatra and the Andaman Islands. Some hours after the earthquake a destructive tsunami followed and hit the coastlines of the surrounding regions, causing widespread destruction in Indonesia, India, Thailand and Sri Lanka. The European Space Agency (ESA) made available a data package composed of European Remote Sensing Satellite Synthetic Aperture Radar (ERS‐SAR) and Environment Satellite Advanced SAR (ENVISAT‐ASAR) data covering the affected area, acquired before (four acquisition dates) and after (five acquisition dates) the earthquake. A total of 26 frames were analysed. We used this dataset to evaluate the effects of the earthquake and tsunami on the human settlements and the physiographic conditions along the coast. The proposed method is based on a visual comparison between pre‐ and post‐seismic SAR intensity images, and on an analysis of their correlation coefficients. No complex data were made available by the ESA to exploit phase coherence. Analysis of pre‐ and post‐earthquake SAR backscattering showed wide uplift areas between the Andaman Islands and Simeulue Island, and large modifications of the coastline of Sumatra. Subsiding areas were detected along the southeast coast of Andaman up to the west coast of Nicobar Island. Tidal effects were filtered out of the SAR images to identify the consequences of the earthquake. Global Positioning System (GPS) stations in the Andaman provided results confirming the surface displacement pattern detected by SAR. The analysis enabled us to draw a boundary line separating the uplift and subsidence.     

Assessment of the ASAR sensor radiometric quality in comparison to ERS‐2 and RADARSAT‐1 SAR data

The estimation of geophysical parameters from Synthetic Aperture Radar (SAR) data necessitates well‐calibrated sensors with good radiometric precision. In this paper, the radiometric calibration of the new Advanced Synthetic Aperture Radar (ASAR‐ENVISAT) sensor was assessed by comparing ASAR data with ERS‐2 and RADARSAT‐1 SAR data. By analysing the difference between radar signals of forest stands, the results show differences of varying importance between the ASAR on the one hand, and the ERS‐2 and the RADARSAT‐1 on the other. For recent data acquired at the end of 2005, the difference varies from ?0.72 to +0.72 dB, with temporal variations that can reach 1.1 dB. For older data acquired in 2003 and 2004, we observe a sharp decrease in the radar signal in the range direction, which can attain 3.5 dB. The use of revised calibration constants provided recently by the European Space Agency (ESA) significantly improves the results of the radiometric calibration, where the difference between the ASAR and the other SARs will be lower than 0.5 dB.     

InSAR time series analysis of the 9 July 1998 Azores earthquake

The 9 July 1998 M_w 6.1 Pico‐Faial earthquake was one of the largest events recorded in the Azores (North Atlantic) in recent years. It generated significant co‐seismic deformation that was captured by a GPS network on Faial Island. On the other islands, where no such networks were available, the co‐seismic surface displacement field was heretofore unknown. To measure it on Pico Island, we analysed Synthetic Aperture Radar (SAR) images using interferometry. Our dataset includes 17 images acquired by the ERS‐1 and ERS‐2 satellites in descending passes between June 1992 and November 2000. The interferograms computed from the available image pairs show poor correlation, particularly over the dense vegetated area of Faial Island and the flanks of Pico Volcano. However, a well‐correlated fringe pattern remains over 33 months for barren parts of NW Pico Island. We analysed phase profiles across this fringe to distinguish the relative contributions of the co‐seismic signal and the tropospheric noise, observing a co‐seismic step of 29±10?mm in range.     

Co‐seismic surface ruptures produced by the 2005 Pakistan M w7.6 earthquake in the Muzaffarabad area,revealed by QuickBird imagery data

High‐resolution QuickBird imagery data have been used to analyse and detect the co‐seismic surface ruptures produced by the 2005 Pakistan M _w7.6 earthquake in the Muzaffarabad area. The analytical results and interpretations of the QuickBird images reveal that the co‐seismic surface ruptures are mostly concentrated on the pre‐existing active faults striking northwest–southeast. Most of co‐seismic surface ruptures show a deformation feature of compressional cracks having a right‐stepping echelon geometric pattern. Individual cracks vary from metre order to 1‐km in length, generally 10 to 100 m. In the northern Muzaffarabad city, an east–west striking co‐seismic surface zone of ～1 km length occurred in the jog area between two northwest–southeast striking surface rupture zones. A strong damage zone along which all buildings completely collapsed is concentrated in a deformation zone of ～60 m wide on the uplift side of the east–west striking surface rupture zone. Large‐scale landslides caused by strong ground motion are mostly constricted on the uplift side along the co‐seismic surface rupture zones. The deformation features and spatial distribution patterns of the co‐seismic surface ruptures and the ground motion direction indicate that the co‐seismic fault that triggered the 2005 Pakistan M _w 7.6 earthquake is a thrust fault with a right‐lateral slip component.     

Co‐seismic ruptures found up to 60 km south of the Kunlun fault after 14 November 2001, Ms 8.1, Kokoxili earthquake using Landsat‐7 ETM+ imagery

A systematic visual interpretation of pre‐ and post‐earthquake Landsat‐7 ETM+ imagery of the 14 November, Ms 8.1 Kokoxili earthquake has revealed significant post‐earthquake lineaments in the region south of the Kunlun fault, which we interpret as co‐seismic surface ruptures related to the event. This previously unreported surface rupturing is located in two broad swathes ～20 and ～60 km south of the main Kunlun fault. Pre‐existing lineaments and subtle tectonic geomorphologic features associated with these ruptures suggest that earthquake‐triggered displacement occurred along pre‐existing faults.     

Mapping hydrologically sensitive areas on the Boreal Plain: a multitemporal analysis of ERS synthetic aperture radar data

Characterizing the spatial and temporal dynamics of hydrologically sensitive areas (HSAs) is vital to the effective management of the boreal forest. HSAs are defined as saturated or inundated areas that, if disturbed, might result in a significant change in the movement of water, nutrients and biota within landscapes. This study presents a remote sensing technique that uses archived European Remote Sensing Satellite (ERS)‐1 and ERS‐2 synthetic aperture radar (SAR) images to monitor HSAs in the Willow River watershed (1030 km²) on the western Boreal Plain of Canada. ERS images were used to generate a probability of HSA occurrence map for a 10‐year period (1991–2000). This map revealed the complexity of HSAs on the western Boreal Plain, where some areas remained consistently dry or wet whereas others were dynamic, transitioning from dry to wet and vice versa. A probability map of HSA occurrence provides spatial and temporal information previously unavailable for this region that may expand our understanding of the hydrological behaviour of drainage basins and serve as a planning tool for land management decisions.     

Measurement of the left‐lateral displacement of Ms 8.1 Kunlun earthquake on 14 November 2001 using Landsat‐7 ETM+ imagery

An imageodesy study has been carried out, using pre‐ and post‐event Landsat‐7 Enhanced Thematic Mapper Plus (ETM+) images, to reveal regional co‐seismic displacement caused by the Ms 8.1 Kunlun earthquake in November 2001. The two Landsat scenes, Kusai Lake and Buka Daban, cover an area of some 57 600 km² (320 km W–E and about 180 km N–S), which includes most of the fault rupture zone. The co‐seismic displacement measured in the Kusai Lake scene shows that the average left‐lateral shift along the Kunlun fault is 4.8 m (ranging from 1.5 to 8.1 m) and the maximum shift appears west of the Kusai Lake. The splayed nature of the fault to the west of Buka Daban, where the fault splits into three branches, causes the displacement pattern to become complicated. Here the average left‐lateral shift, between the south side of the southern branch and the north side of the northern branch, is 4.6 m (ranging from 1.0 to 8.2 m). Our results also illustrate that the south side of the fault is the ‘active’ block, moving significantly in an east–south‐easterly direction, relative to the largely ‘stable’ northern block.     

Observations of ice surface temperature and thickness in the Baltic Sea

This paper presents the results of an airborne thermal infrared (TIR) experiment. The data were obtained during 6–9 February 1992 period in the Bay of Bothnia, the northern section of the Baltic Sea, in connection with an ERS‐1 field campaign. Two Aegema model 880 TIR cameras were used with nominal wavelengths at 5 and 10 µm, attached to the front of the helicopter with a Tyler mount. The camera's thermal resolution is 0.2 K; after corrections for atmosphere effects, the surface temperature accuracy is 0.5 K. The spatial resolution of individual images is 70 cm at the 300‐m flight altitude. The measurement programme was successful, producing high‐quality TIR data over ice for two different days, even under difficult weather conditions. Ice temperatures ranged from open water temperatures to 261 K for fast ice conditions on the day on the first flight. The standard deviation of the surface temperature, generally, increased with ice thickness with a value of ～0.4 K for maximum thickness, and autocorrelation length scales not exceeding a value of 5 m. Generally, all the higher values of standard deviation (>0.7) of surface temperatures were for scenes with mixed ice/open water. The results show that TIR has a substantial ability to classify ice type and thickness when the air temperature is less than 269 K, from open water at the freezing point to thin nilas and thicknesses up to 20–45 cm in the fast ice zone. In addition, a quasi‐steady sea‐ice model is used to provide a physical interpretation of the sea‐ice surface temperatures. The use of the model requires information on the atmospheric surface layer and snow thickness data, together with calibration points. The model worked well when the air temperature was around 260 K or less.     

Deformation monitoring over large areas with multipass differential SAR interferometry: a new approach based on the use of spatial differences

Multipass differential synthetic aperture radar interferometry is becoming increasingly important as a powerful technique for ground deformation retrieval compared with classical geodetic techniques such as levelling and global positioning system (GPS). It proves superior in terms of costs, coverage, data accessibility and availability of historical archives. Application to different areas of risk management such as monitoring of volcanoes and slope instabilities, tectonic movements, urban areas and infrastructure, has already been successfully demonstrated. In this work we discuss a new multipass differential synthetic aperture radar interferometry processing technique that makes extensive use of spatial differences. The results obtained demonstrate that this technique allows the monitoring of ground deformation over wide areas. The processed data were acquired from ERS–1 and ERS–2 sensors over three partially overlapping tracks related to a region, approximately 240 km N–S and 80 km E–W wide, located in the centre‐south of Italy, along the west coast. Comparison of the mean deformation velocity results over the different tracks and of the deformation evolution with levelling measures, available in some areas, shows good agreement and goes to validate the technique.     

Hyperspectral indices to diagnose leaf biotic stress of apple plants,considering leaf phenology

Novel and existing hyperspectral vegetation indices were evaluated in this study, with the aim of assessing their utility for accurate tracking of leaf spectral changes due to differences in biophysical indicators caused by apple scab. Novel indices were extracted from spectral profiles by means of narrow‐waveband ratioing of all possible two‐band combinations between 350 nm and 2500 nm at nanometer intervals (2 311 250 combinations) and all possible two‐band derivative combinations. Narrow‐waveband ratios consisting of wavelengths of approximately 1500 nm and 2250 nm, associated with water content, have proven to be the most appropriate for detecting apple scab at early developmental stages. Logistic regression c‐values ranged from 0.80 to 0.88. At a more developed infection stage, vegetation indices such as R₄₄₀/R₆₉₀ and R₆₉₅/R₇₆₀ exhibited superior distinction between non‐infected and infected leaves. Identified derivative indices were located in similar regions. It therefore was concluded that the most appropriate indices at early stages of infection are ratios of wavelengths situated at the water band slopes. The choice of appropriate indices and their discriminatory performances, however, depended on the phenological stage of the leaves. Hence, an undisturbed 20‐day growth profile was examined to assess the effect of physiological changes on spectral variations at consecutive growth stages of leaves. Results suggested that an accurate distinction could be made between different leaf developmental stages using the 570 nm, 1460 nm, 1940 nm and 2400 nm wavelengths, and the red‐edge inflection point. These results are useful to crop managers interested in an early warning system to aid proactive system management and steering.     

Coseismic deformation and source model of the 12 November 2017 MW 7.3 Kermanshah Earthquake (Iran–Iraq border) investigated through DInSAR measurements

A large earthquake with a magnitude of M_W 7.3 struck the border of Iran and Iraq at the province of Kermanshah, Iran. In our study, coseismic deformation and source model of the 12 November 2017 Kermanshah Earthquake are investigated using ALOS-2 ScanSAR and Sentinel-1A/B TOPSAR Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques. Geodetic inversion has been performed to constrain source parameters and invert slip distribution on the fault plane. The optimised source model from joint inversion shows a blind reverse fault with a relatively large right-lateral component, striking 353.5° NNW-SSE and dipping 16.3° NE. The maximum slip is up to 3.8 m at 12–14 km depth and the inferred seismic moment is 1.01 × 10²⁰ Nm, corresponding to M_W 7.3, consistent with seismological solutions. The high-resolution optical images from SuperView-1 satellite suggest that most of the linear surface features mapped by DInSAR measurements are landslides or surface cracks triggered by the earthquake. Coulomb stress changes on the source fault indicating consistency between aftershock distribution and high loaded stress zones. Based on the stress change on neighbouring active faults around this area, the Kermanshah Earthquake has brought two segments of the Zagros Mountain Front Fault (MFF), MFF-1 and MFF-2, 0.5–3.1 MPa and 0.5–1.96 MPa closer to failure, respectively, suggesting the risk of future earthquakes. Recent major aftershocks (M_W≥ 5.0) could probably ease the seismic hazard on MFF-2, but the risk of earthquakes on MFF-2 is still increasing.     

Two‐scale surface deformation analysis using the SBAS‐DInSAR technique: a case study of the city of Rome,Italy

We have exploited the capability of the differential synthetic aperture radar (SAR) interferometry (DInSAR) technique, referred to as Small BAseline Subset (SBAS) approach, to analyse surface deformation at two distinct spatial scales: a low resolution, large scale, and a fine resolution, local scale. At the large scale, the technique investigates DInSAR data with a ground resolution of the order of 100 m×100 m and leads to generate mean deformation velocity maps and associated time series for areas extending to some thousands of square kilometres. At the local scale, the technique exploits the SAR images at full spatial resolution (typically of the order of 5 m×20 m), detecting and analysing localized deformation phenomena. The study is focused on the city of Rome, Italy, and we used the ERS‐1/2 satellite radar data relevant to the 1995–2000 time period. The presented results demonstrate the capability of the SBAS approach to retrieve, from the low‐resolution DInSAR data, large‐scale deformation information leading to identify several sites affected by significant displacements. Our analysis permitted us to conclude that a major contribution to the detected displacements is due to the consolidation of the alluvial soils present in the area, mostly enforced by the buildings' overload. Furthermore, in a selected area, a detailed analysis was carried out by exploiting the full resolution DInSAR data. In this case we investigated deformation phenomena at the scale of single buildings. As key result we showed that differential displacements of few mm a^?1, affecting single man‐made structures or building complexes, could be detected, thus allowing to identify sites that may potentially be involved in critical situations.     

Deformation retrieval in large areas based on multibaseline DInSAR algorithm: a case study in Cangzhou,northern China

The DInSAR technique with a multibaseline is becoming popular nowadays to investigate slow urban deformation. In this paper, we focus on deformation retrieval in large areas, including urban and suburban areas. Based on the multibaseline DInSAR algorithm proposed by Mora, three extensions are derived. First, least‐squares adjustment and error‐controlling methods are used to obtain stable deformation velocity and height error estimations. The least‐squares QR factorizaiton algorithm is emphasized to solve large, linear, and sparse functions. Second, a new complex network is presented to limit noise effects on the Delaunay triangular network. Third, by combining complex and Delaunay networks, large‐area deformation is investigated, from centre urban areas to suburban areas. The enhanced algorithm is performed to investigate the subsidence of Cangzhou, Hebei province (northern China) during 1993–1997 by using 9 ERS SLC data. The experimental results show serious subsidence in the region and are validated by levelling data and groundwater wells data. Compared with levelling data, the estimation errors of linear deformation velocity in urban areas are in the range of (?2, 2) mm year^?1, and in suburban areas, the errors are in the range of (?26, 15) mm year^?1, which is sufficiently feasible to determine the status of subsidence relative to the maximum deformation velocity of about ?100 mm year^?1. The subsidence centres in urban areas are consistent with the spatial distribution of groundwater wells, which provides evidence that groundwater overexploitation is the main cause of subsidence in Cangzhou. The closure of wells will be a good way to control subsidence in the future.     

Estimation of chlorophyll‐a concentration in Lake Tai,China using in situ hyperspectral data

Reflectance spectra of water in Lake Tai of East China were measured at 28 monitoring stations with an ASD FieldSpec spectroradiometer at an interval of 1.58 nm over five days in each month from June to August of 2004. Water samples collected at these stations were analyzed in the laboratory to determine chlorophyll‐a (chl‐a) concentration. Twenty‐eight spectral reflectance curves were standardized and correlated with chl‐a concentration. Examination of these curves reveals a peak reflectance at 719 nm. Chl‐a concentration level in the Lake was most closely correlated with the reflectance near 700 nm. If regressed against the reflectance at the wavelength of 667 nm (R ₆₆₇), chl‐a concentration was not accurately estimated at R ² = 0.494. Accuracy of estimation was improved to R ² = 0.817 using the maximum reflectance. A higher accuracy of 0.837 was achieved using the peak reflectance at 719 nm (R ₇₁₉) because it does not drift with the level of chl‐a concentration. The highest accuracy of estimation was achieved at R ² = 0.868 using R ₇₁₉/R ₆₆₇.     

Evaluation of MODIS ocean colour products at a northeast United States coast site near the Martha's Vineyard Coastal Observatory

Moderate Resolution Imaging Spectroradiometer (MODIS) marine and atmospheric products were evaluated using match‐ups of MODIS and in situ measurements collected by an above‐water radiometric system, the SeaWiFS Photometer Revision for Incident Surface Measurements (SeaPRISM), deployed near the Martha's Vineyard Coastal Observatory from 2004 to 2005. The products evaluated include the normalized water‐leaving radiance L _wn in the visible and near‐infrared bands, and the aerosol optical thickness at 870 nm τ_a(870), and the Ångström exponent α(531). With a restricted match‐up criterion, the result shows that the MODIS‐retrieved L _wn at 488, 531 and 551 nm agree very well with SeaPRISM measurements, giving mean per cent differences δ(%) of 3–7%, absolute mean per cent differences |δ|(%) of ～16%, and coefficient of determination R ² of 0.84–0.88. However, the MODIS‐retrieved L _wn at 412 nm are underestimated significantly with δ(%), |δ|(%) and R ² of ?35%, 57% and 0.32, respectively, corresponding to a consistent overestimation and underestimation for the MODIS‐retrieved τ_a(870) and α(531), respectively. Temporal patterns of match‐ups revealing two distinct cases of the discrepancy of MODIS retrievals from in situ SeaPRISM measurements are discussed.     

The positive temperature anomaly as detected by Landsat TM data in the eastern Marmara Sea (Turkey): possible link with the 1999 Izmit earthquake

A long (～15 km) and narrow (～4 km) offshore positive temperature anomaly (～1.7° C) is observed in the Landsat Thematic Mapper (TM) thermal infrared (TIR) image acquired the day following the large ?zmit earthquake (Mw 7.4) of 17 August 1999, in eastern Marmara Sea, Turkey. The earthquake was generated along the North Anatolian Fault, which ruptured for about 150 km, and the anomaly formed at the western termination of this rupture. Discussions of this anomaly may develop by processes different than the seismic activity and considerations on fault geometry and sea bathymetry characteristics suggest that the anomaly may result from aftershock activity near the western end of the earthquake fault. The formation of the anomaly requires the addition of a large quantity of hot waters to the sea. The ascent to the sea bottom of fault‐driven hot fluids (seismic pumping) and formation of thermal plumes may be the processes by which the sea surface temperature increased. Recent works and the present study suggest that TIR data analysis may be used as a tool in seismological studies.     

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXT_PPE and GXT_PT). Maximal oxygen consumption (VO_2max) during GXT_PPE was 17.3% lower than the GXT_PT in regular exercise clothing (43.0 ± 5.7 vs. 52.4 ± 8.5 ml/kg per min, respectively). The lower VO_2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 ± 18.0 vs. 167.1 ± 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 ± 10.4 vs. 3.2 ± 0.4 l). Breathing frequency at peak exercise was unchanged (55 ± 7 vs. 53 ± 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO_2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.     

Evaluation of the B‐method for determining actual evapotranspiration in a boreal forest from MODIS data

Boreal forests occupy about 11% of the terrestrial surface and represent an important contribution to global energy balance. The ground measurement of daily evapotranspiration (LE_d) is very difficult due to the limitations on experiments. The objective of this paper is to present and explore the applicability of the B‐method for monitoring actual LE_d in these ecosystems. The method shown in this paper allows us to determine the surface fluxes over boreal forests on a daily basis from instantaneous information registered in a conventional meteorological tower, as well as the canopy temperature (T _c) retrieved by satellite. Images collected by the MODIS (moderate resolution imaging spectroradiometer) on board EOS‐Terra have been used for this study. The parameters of the model were calibrated from the SIFLEX‐2002 (Solar Induced Fluorescence Experiment 2002) campaign dataset in a northern boreal forest in Finland. A study of these parameters was made on an hourly basis in order to make the method applicable, not only at midday but within an interval of 7 h around it. This is an important advance with respect to the original formulation of this approach since the overpass time of satellites can be very variable. The comparison between T _c ground measured with a thermal infrared radiometer, and T _c retrieved from land surface temperature (LST) MODIS data, showed an estimation error of ±1.4°C for viewing angles from 5 to 60°. A complete sensitivity analysis was carried out and an estimation error of about ±35%, corresponding to the interval 10.00–11.00 h UTC, was shown as the lowest in LE_d retrieval. Finally, the method was validated over the study site using 21 MODIS images for 2002 and 2003. The results were compared with eddy‐correlation ground measurements. An accuracy of ±1.0 mm/day and an overestimation of 0.3 mm/day were shown in the LE_d retrieval.     

The energetics of walking on sand and grass at various speeds

This study investigated the energetics of walking on sand and grass. Fourteen adult males, participated in the study. Participants had a mean age of 34.6 years old, 72.6 kg in mass and 172.5 cm in stature, who walked at 3, 4, 5, 6 and 7 km per h on sand and grass surfaces. Physiological measures included heart rate, O₂ uptake, CO₂ exhalation, ventilation and relative O₂ uptake using a MetaMax Ergospirometer. Speed was controlled in a methodology similar to the ‘Multistage 20-m Shuttle Run Test’. Data were collected during physiological steady rate at each determined speed. A minimum of 2 h rest was enforced between randomized conditions. Results indicate that there was a significant increase (p < 0.01) in all measured physiological indices indicative of energy expenditure when walking on sand compared to grass at 3–7 km per h, with the greatest disparity between the surfaces (ratio = 1.63) in relative O₂ consumption at 5 km per h.