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Indonesia is an archipelago country with great potential for marine renewable energy, particularly for wave energy. This study will provide a wave energy assessment of Indonesia over a 6.5-year period (2011–2017) with resolution about 5.5 km. This assessment is based on data generated with a two-way nested high-resolution wave model WAVEWATCH III with observation-based physics (ST6). Three grids have been generated, namely a 'high resolution' of 3 arc-minute (0.05°) grid is nested inside a 12 arc-minute (0.2°) grid which is nested within a 0.5° global grid. Validations against altimeters and buoys show good agreement with the model. Mean wave energy has been classified based on meteorological seasons and it is found that the most energetic months are June, July, August for all areas of south, southwest and west of Indonesia where it can exceed 30 kW/m. In some locations wave energy is available throughout the entire year, that is in the south of Jawa island, Bali island and West Nusa Tenggara while in the region of west Sumatera, promising wave energy is available during the time from March to November. In addition, within the Indonesian Archipelago the monthly variations are about 5 kW/m and relatively small in terms of absolute values but this region is large relative to the mean wave power energy. • Wave energy assessment for Indonesian archipelago with spatial resolution of 0.05°. • Based on a dynamically downscaled wave model with observation-based physics (ST6). • Mean wave power in excess of 30 kW/m was found for season June to August. • 10% of mean wave power exceeds 40 kW/m with the top-one percent up to 60 kW/m. [ABSTRACT FROM AUTHOR]

Hai Yang-2 ( HY-2) satellite altimeter measurements of significant wave height () are analyzed over the period from 1 October 2011 to 6 December 2014. They are calibrated and validated against in situ buoys and other concurrently operating altimeters: Jason-2, CryoSat-2, and Satellite with Argos and ALtiKa ( SARAL). In general, the HY-2 altimeter measurements agree well with buoy measurements, with a bias of −0.22 m and a root-mean-square error (RMSE) of 0.30 m. When the reduced major axis (RMA) regression procedure was applied to the entire period, the RMSE was reduced by 33% to 0.2 m. A further comparison with other satellite altimeters, however, revealed two additional features of HY-2 estimates over this period. First, a noticeable mismatch is present between HY-2 and the other satellite altimeters for high seas ( > 6 m). Second, a jump increase in HY-2 values was detected starting in April 2013, which was associated with the switch to backup status of the HY-2 sensors and the subsequent update of its data processing software. Although reported by previous studies, these two deficiencies had not been accounted for in calibrations. Therefore, the HY-2 wave height records are now subdivided into two phases (time periods pre- and post-April 2013) and a two-branched calibration is proposed for each phase. These revised calibrations, validated throughout the range of significant wave heights of 1-9 m, are expected to improve the practical applicability of HY-2 measurements significantly. [ABSTRACT FROM AUTHOR]

Altimeter data from transects across the Southern Ocean are analyzed to determine the decay of oceanic swell. The resulting decay rate is shown to be proportional to wavenumber squared and swell amplitude cubed. Such a decay relationship is consistent with turbulent interaction with the background, either in the air or water. The present data cannot distinguish between these two cases. The results are consistent with the limited previous studies and present a source term suitable for use in wave prediction models. [ABSTRACT FROM AUTHOR]

Down-looking laser altimeters are commonly used to measure the sea surface elevation. However, because the laser radiation is attenuated by spray droplets suspended along the transmission path, it is presumed that altimeters may also provide an indirect measure of the sea spray volume. Here, this conjecture is discussed by means of laboratory experiments, which have been conducted in a wind-wave flume. A large number of wind conditions were considered between equivalent 10-m wind speeds of 20 and 60 m s−1 in order to generate different spray volumes above the water surface. The facility was equipped with a laser and side-looking camera system to estimate the spray volume as well as a nearby down-looking laser altimeter. Results confirm that there is a robust degradation of the laser intensity for increasing wind speed and hence the amount of spray droplets above the water surface. A simple regression model to extract spray volume from the average intensity of the laser radiation is presented, demonstrating the promise of laser altimeters for making in situ spray observations. Additional observations will be required to calibrate the altimeters for applications in the open ocean marine environment. [ABSTRACT FROM AUTHOR]

Reliable estimates of ocean surface waves and their long-term global trends are fundamentally important for numerous ocean engineering and geophysical applications. Nonetheless, it is scientifically and technically demanding to accurately identify such relatively small trends [ O (0. 1 − 1) cm yr−1] from wave data currently available. In 2022, Young and Ribal demonstrated that by changing the calibration method, multiplatform altimeter observations yield noticeable differences in wave height estimates and their trends. In this paper, we use our global wave hindcast as a baseline and confirm that observations calibrated relative to one another (i.e., "altimeter-altimeter" calibration) ultimately outperform traditionally "altimeter-buoy" calibrated data. The former leads to more consistent mean and extreme wave heights across simultaneously operating altimeters and consequently to a more homogeneous evolution of global sea states over the past several decades. The underlying reason is hypothesized to be that temporal inhomogeneities in long-term NDBC buoy records due to changes in buoy hardware and software over time introduce comparable inhomogeneities to long-term altimeter observations when the "altimeter-buoy" calibration is adopted. It is encouraging to observe that the global trends of mean and 90th-percentile wave heights over the period 1992-2019 from our hindcast and re-calibrated altimeter data are very close: approximately 0.3 cm yr−1. Nonetheless, the altimeter-based trend of 99th-percentile wave height, H s 99 , is substantially-but-spuriously stronger mainly due to markedly growing availability of altimeter missions over time. Our work clearly demonstrates the power of third generation spectral wave models as diagnostics tools. Given the uncertainties embedded in buoy and satellite observations, wave modeling and global wave hindcasts can indeed guide these measurements. Further analysis of the underlying climate physics driving the interannual variability of ocean waves in wind-sea dominated regions is also presented. • Investigation of global wave height climatology and trends from altimeter and model. • Intercomparison of two calibration methods of altimeter wave observations. • The "altimeter-altimeter" calibration outperforms the "altimeter-buoy" calibration. • Inhomogeneity clearly exists in the long-term NDBC buoy records. • Impact of large-scale climate physics on the interannual variability of ocean waves. [ABSTRACT FROM AUTHOR]