Earth’s gravity field modelling based on satellite accelerations derived from onboard GPS phase measurements

<p>GPS data collected by satellite gravity missions can be used for extracting the long-wavelength part of the Earth’s gravity field. We propose a new data processing method which makes use of the ‘average acceleration’ approach to gravity field modelling. In this method, satellite accelerations are directly derived from GPS carrier phase measurements with an epoch-differenced scheme. As a result, no ambiguity solutions are needed and the systematic errors that do not change much from epoch to epoch are largely eliminated. The GPS data collected by the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission are used to demonstrate the added value of the proposed method. An analysis of the residual accelerations shows that accelerations derived in this way are more precise, with noise being reduced by about 20 and 5% at the cross-track component and the other two components, respectively, as compared to those based on kinematic orbits. The accelerations obtained in this way allow the recovery of the gravity field to a slightly higher maximum degree compared to the solution based on kinematic orbits. Furthermore, the gravity field solution has an overall better performance. Errors in spherical harmonic coefficients are smaller, especially at low degrees. The cumulative geoid height error is reduced by about 15 and 5% up to degree 50 and 150, respectively. An analysis in the spatial domain shows that large errors along the geomagnetic equator, which are caused by a high electron density coupled with large short-term variations, are substantially reduced. Finally, the new method allows for a better observation of mass transport signals. In particular, sufficiently realistic signatures of regional mass anomalies in North America and south-west Africa are obtained.</p

The causes of early 2022 fires in Corrientes province

El fuego es una herramienta de manejo del pastizal natural en la provincia de Corrientes; se utiliza regularmente para eliminar la biomasa muerta en pie, con el fin de promover un mayor crecimiento estival. Sin embargo, y aunque no existen estadísticas sobre el uso estacional del fuego, a principios de 2022, los incendios naturales o inducidos afectaron más de 10000 km2, en el pico de la temporada de crecimiento. Este trabajo cuantifica las áreas afectadas por los incendios en esa provincia durante enero y febrero de 2022, y analiza la contribución de factores naturales y antrópicos a la extensión del área que afectó el fuego. Usamos la plataforma Google Earth Engine para identificar y clasificar el área quemada usando imágenes satelitales Sentinel. Además, mediante análisis de regresión simple y múltiple evaluamos la relación entre factores naturales y antrópicos y el área afectada por los incendios. Las áreas quemadas representaron ~12% de toda la provincia. La cobertura del suelo más afectada fueron los humedales. Las evidencias indicaron que la disminución de la superficie de agua y la proporción de áreas protegidas se relacionaron directa y positivamente con la extensión de las áreas quemadas. Por otra parte, la carga animal y la red vial se relacionaron de forma inversa y negativa con el área quemada. La predicción de los patrones de fuego es esencial para desarrollar políticas de gestión para prevenir o morigerar eventos catastróficos similares.Fire is a natural grassland management tool, often used to eliminate the standing dead biomass and promote growth before the growing season. However, while there is a lack of data on the seasonal use of fire in the province of Corrientes, natural and induced fires in early 2022 affected over 10000 km2 at the peak of the growing season. This paper quantifies the extent of the fire-affected area in Corrientes during January and February 2022 and analyzes the contribution of natural and anthropogenic factors to the extent of the fire-affected area. We used the Google Earth Engine platform to identify and classify burnt areas using Sentinel satellite images, and applied simple and multiple regression analysis to investigate the contribution of natural and anthropogenic factors to the extent of the fire-affected area. Results show that 12% of Corrientes was affected by fire during the study period, with wetlands being the most affected land cover type. This study provides evidence of the relationship between natural and anthropogenic factors and the fires that affected Corrientes at the beginning of 2022. The results show that the reduction of water area and protected areas was positively and directly related to the extent of burnt areas, while the road network and livestock density were inversely and negatively related to the burned area size. Predicting fire patterns is essential to develop management policies to prevent or reduce the impact of future catastrophic events.Fil: Saucedo, Griselda Isabel. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Corrientes. Estación Experimental Agropecuaria Corrientes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Perucca, Alba R.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Corrientes. Estación Experimental Agropecuaria Corrientes; ArgentinaFil: Kurtz, Ditmar Bernardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Corrientes. Estación Experimental Agropecuaria Corrientes; Argentin

Seasonal mass variations show timing and magnitude of meltwater storage in the Greenland Ice Sheet

The Greenland Ice Sheet (GrIS) is currently losing ice mass. In order to accurately predict future sea level rise, the mechanisms driving the observed mass loss must be better understood. Here, we combine data from the satellite gravimetry mission Gravity Recovery and Climate Experiment (GRACE), surface mass balance (SMB) output of the Regional Atmospheric Climate Model v. 2 (RACMO2), and ice discharge estimates to analyze the mass budget of Greenland at various temporal and spatial scales. We find that the mean rate of mass variations in Greenland observed by GRACE was between −277 and −269 Gt yr−1 in 2003–2012. This estimate is consistent with the sum (i.e., −304±126 Gt yr−1) of individual contributions – surface mass balance (SMB, 216±122 Gt yr−1) and ice discharge (520±31 Gt yr−1) – and with previous studies. We further identify a seasonal mass anomaly throughout the GRACE record that peaks in July at 80–120 Gt and which we interpret to be due to a combination of englacial and subglacial water storage generated by summer surface melting. The robustness of this estimate is demonstrated by using both different GRACE-based solutions and different meltwater runoff estimates (namely, RACMO2.3, SNOWPACK, and MAR3.9). Meltwater storage in the ice sheet occurs primarily due to storage in the high-accumulation regions of the southeast and northwest parts of Greenland. Analysis of seasonal variations in outlet glacier discharge shows that the contribution of ice discharge to the observed signal is minor (at the level of only a few gigatonnes) and does not explain the seasonal differences between the total mass and SMB signals. With the improved quantification of meltwater storage at the seasonal scale, we highlight its importance for understanding glacio-hydrological processes and their contributions to the ice sheet mass variability

Orbital Gravity Gradiometry Beyond GOCE: Mission Concepts

Significant advances in the technologies needed for space-based cryogenic instruments have been made in the last decade, including cryocoolers, spacecraft architectures and cryogenic amplifiers. These enable considerably more complex instruments to be put into orbit for long-duration missions. One such instrument is the Superconducting Gravity Gradiometer (SGG) developed by Paik, et al. A magnetically levitated version is under consideration for a follow-on mission to GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity field and steady-state Ocean Circulation Explorer). With its inherently greater rejection of common mode accelerations and ability to cancel the coupling of angular accelerations into the gradient signal, the SGG can achieve [an accuracy of] 0.01 milli-Eotvos (gravitational gradient of the Earth) divided by the square root of frequency in hertz, with requirements for attitude control that can be met with existing spacecraft. In addition, the use of a cryocooler for cooling the instrument will alleviate the previously severe constraint on mission lifetime imposed by the use of superfluid helium,. enabling mission durations in the 5-10 year range. Studies are underway to determine requirements for orbit (polar versus sun-synchronous), altitude (which affects spacecraft drag), instrument temperature and stability, cryocooler vibration control, and control and readout electronics. These will be used to determine the SGG's sensitivity and ultimate resolution for gravity recovery. This paper will discuss preliminary instrument and spacecraft design, and toplevel mission requirements

Evaluating GRACE Mass Change Time Series for the Antarctic and Greenland Ice Sheet—Methods and Results

Satellite gravimetry data acquired by the Gravity Recovery and Climate Experiment (GRACE) allows to derive the temporal evolution in ice mass for both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS). Various algorithms have been used in a wide range of studies to generate Gravimetric Mass Balance (GMB) products. Results from different studies may be affected by substantial differences in the processing, including the applied algorithm, the utilised background models and the time period under consideration. This study gives a detailed description of an assessment of the performance of GMB algorithms using actual GRACE monthly solutions for a prescribed period as well as synthetic data sets. The inter-comparison exercise was conducted in the scope of the European Space Agency’s Climate Change Initiative (CCI) project for the AIS and GIS, and was, for the first time, open to everyone. GMB products generated by different groups could be evaluated and directly compared against each other. For the period from 2003-02 to 2013-12, estimated linear trends in ice mass vary between −99 Gt/yr and −108 Gt/yr for the AIS and between −252 Gt/yr and −274 Gt/yr for the GIS, respectively. The spread between the solutions is larger if smaller drainage basins or gridded GMB products are considered. Finally, findings from the exercise formed the basis to select the algorithms used for the GMB product generation within the AIS and GIS CCI project