GRACE gravity solutions validated by in-situ ocean bottom pressure in different regions of the global ocean

The GRACE satellite mission provides gravity field estimates of the Earth with unprecedented accuracy. Nevertheless,the realistic detection of oceanic mass redistribution remains challenging due to comparatively small signalamplitude, aliasing by tides and other short-term variability, and smoothing of small spatial scales. To verify thecapability of GRACE to measure oceanic mass variability, a validation with in-situ timeseries of Ocean BottomPressure (OBP) timeseries is essential.Here, different GRACE gravity fields provided by the GRACE Science Data System (CSR, GFZ, JPL), GRGS,ITG and others are compared with more than 140 timeseries of OBP sensors deployed throughout all oceans.The performance of the different GRACE products to capture oceanic mass variability is assessed by a weighedcorrelation analysis, taking into account the length and data quality of the in-situ time series. Both Gaussianfiltering and an ocean-model derived spatial pattern filtering method are used for the GRACE data, whereas forthe in-situ timeseries, different de-tiding and de-trending methods are applied to reduce aliasing and sensor drift.The analysis aims (a) to quantify the skill of different GRACE products and to quantify the advances made byrecent GRACE gravity field releases with improved data processing, and (b) to identify regions where GRACEperforms exceptionally well (e.g. high latitudes), and in which parts of the oceans GRACE fails to detect real OBPvariability. Spatial patterns related to the performance of GRACE may help to predict the quality of spacebornegravity measurements also for those oceanic regions where no in-situ data are available. This is critical for thefuture use of GRACE to remotely determine water mass redistribution in all oceans

The Utah Statesman, September 22, 2016

Weekly student newspaper of Utah State University in Logan.https://digitalcommons.usu.edu/newspapers/1344/thumbnail.jp

A global Ocean Bottom Pressure data base as ground-truth reference for GRACE gravity field products

The GRACE satellite mission provides monthly estimates of the gravity field of the Earth. Differences between the monthly solutions are induced by mass redistribution on the Earth. Over the continents, the hydrological cycle represents the largest signals, which are readily observed by GRACE. Over the oceans, however, gravity field changes are about an order of magnitude smaller, close to the accuracy limits of the present GRACE solutions. Nevertheless, GRACE measurements may prove as an important tool to obtain integral estimates of water mass redistribution, sea level changes and geostrophic current variability. In order to validate and improve the gravity field products, GRACE is to be compared against ocean models and in-situ observations of Ocean Bottom Pressure (OBP). Time series of OBP sensors deployed by Alfred-Wegener-Institut in the Antarctic Circumpolar Current, as well as measurements from other locations of the global ocean are included in a OBP database that is currently under development at AWI, in close cooperation with Proudman Oceanographic Laboratory (POL, Liverpool). The mutual comparison of in-situ and ocean model data with different GRACE products provided by CSR, GFZ, GRGS, ITG and JPL will help to optimize data processing methods and corrections applied to GRACE, and to identify the performance of GRACE to detect oceanic mass flux variability in different regions of the global ocean

Marine soundscape planning: Seeking acoustic niches for anthropogenic sound

Both marine mammals and hydroacoustic instruments employ underwater sound to communicate, navigate or infer information about the marine environment. Concurrent timing of acoustic activities using similar frequency regimes may result in (potentially mutual) interference of acoustic signals when both sources are within audible range of the recipient. While marine mammal fitness might be negatively impacted upon, both on individual and population level, hydroacoustic studies may generate low quality data or suffer data loss as a result of bioacoustic interference. This article pursues, in analogy to landscape planning, the concept of marine soundscape planning to reconcile potentially competing uses of acoustic space by managing the anthropogenic sound sources. We here present a conceptual framework exploring the potential of soundscape planning in reducing (mutual) acoustic interference between hydroacoustic instrumentation and marine mammals. The basis of this framework is formed by the various mechanisms by which acoustic niche formation (i.e., the partitioning of the acoustic space) occurs in species-rich communities that acoustically coexist while maintaining high fidelity (hi-fi) soundscapes, i.e., by acoustically partitioning the environment on the basis of time, space, frequency and signal structure. Hydroacoustic measurements often exhibit certain flexibility in their timing, and even instrument positioning, potentially offering the opportunity to minimize the ecological imprint of their operation. This study explores how the principle of acoustic niches could contribute to reduce potential (mutual) acoustic interference based on actual acoustic data from three recording locations in polar oceans. By employing marine soundscape planning strategies, entailing shifting the timing or position of hydroacoustic experiments, or adapting signal structure or frequency, we exemplify the potential efficacy of smart planning for four different hydroacoustic instrumentation types: multibeam echosounders, air guns, RAFOS (Ranging and Fixing of Sound) and tomographic sound sources