Abstract
This paper proposes a 2D notch generator algorithm based on frequency-invariant (FI)-shaped beampattern synthesis for the Global Navigation Satellite System (GNSS) space–time anti-jamming blind null-steering mode. Unlike conventional blind null-steering anti-jamming algorithms based on the power inversion (PI) algorithm, the developed method treats the blind null-steering spatial filter as a 2D spatial notch filter. The beampattern synthesis method is used to solve the value of the space–time filter. With the jamming direction as prior information, constraints are applied to the flat-top (FT) and nulling (NL) regions, and FI-shaped constraints are added to the FT region to establish the objective function. NL and FI enhancement coefficients are introduced to ensure the convergence speed of the objective function and the depth of nulling. The optimization method based on the alternating direction multiplier method is employed to solve the objective function. This synthesis method is applicable to arbitrary antenna arrays. The simulation shows that compared with the PI-based algorithms, the proposed algorithm ensures undistorted reception of GNSS signals, considerably improves the receiver’s signal-to-jamming-noise ratio in different jamming scenes, enhances anti-jamming ability, and achieves an improvement of better than 20 dB in multiple three-jamming scenes.
A rock formation spanning Ireland and Scotland may be the world's most complete record of "snowball Earth," a crucial moment in planetary history when the globe was covered in ice, finds a new study led by UCL (University College London) researchers.
The Yukon River flows west across Alaska toward the Bering Sea, eroding Arctic permafrost along its banks and transporting sediment downstream. Within that sediment lurks a toxic stowaway: mercury.
This Dec. 27, 2023 image of the São Francisco River in southeast Brazil showcases the range of vibrant colors in the area including blues, reds, greens, and yellows. Much of the unvegetated land, such as unplanted fields and unpaved roads, appears in bright shades of red and yellow. This coloration comes from the underlying clays and soils of Brazil's state of Minas Gerais.
Implementation of a brittle sea ice rheology in an Eulerian, finite-difference, C-grid modeling framework: impact on the simulated deformation of sea ice in the Arctic
Laurent Brodeau, Pierre Rampal, Einar Ólason, and Véronique Dansereau
Geosci. Model Dev., 17, 6051–6082, https://doi.org/10.5194/gmd-17-6051-2024, 2024
A new brittle sea ice rheology, BBM, has been implemented into the sea ice component of NEMO. We describe how a new spatial discretization framework was introduced to achieve this. A set of idealized and realistic ocean and sea ice simulations of the Arctic have been performed using BBM and the standard viscous–plastic rheology of NEMO. When compared to satellite data, our simulations show that our implementation of BBM leads to a fairly good representation of sea ice deformations.
A simple approach to represent precipitation-derived freshwater fluxes into nearshore ocean models: an FVCOM4.1 case study of Quatsino Sound, British Columbia
Krysten Rutherford, Laura Bianucci, and William Floyd
Geosci. Model Dev., 17, 6083–6104, https://doi.org/10.5194/gmd-17-6083-2024, 2024
Nearshore ocean models often lack complete information about freshwater fluxes due to numerous ungauged rivers and streams. We tested a simple rain-based hydrological model as inputs into an ocean model of Quatsino Sound, Canada, with the aim of improving the representation of the land–ocean connection in the nearshore model. Through multiple tests, we found that the performance of the ocean model improved when providing 60 % or more of the freshwater inputs from the simple runoff model.
TAMS: a tracking, classifying, and variable-assigning algorithm for mesoscale convective systems in simulated and satellite-derived datasets
Kelly M. Núñez Ocasio and Zachary L. Moon
Geosci. Model Dev., 17, 6035–6049, https://doi.org/10.5194/gmd-17-6035-2024, 2024
TAMS is an open-source Python-based package for tracking and classifying mesoscale convective systems that can be used to study observed and simulated systems. Each step of the algorithm is described in this paper with examples showing how to make use of visualization and post-processing tools within the package. A unique and valuable feature of this tracker is its support for unstructured grids in the identification stage and grid-independent tracking.
Global sensitivity analysis of simulated remote sensing polarimetric observations over snow
Matteo Ottaviani, Gabriel Harris Myers, and Nan Chen
Atmos. Meas. Tech., 17, 4737–4756, https://doi.org/10.5194/amt-17-4737-2024, 2024
We analyze simulated polarization observations over snow to investigate the capabilities of remote sensing to determine surface and atmospheric properties in snow-covered regions. Polarization measurements are demonstrated to aid in the determination of snow grain shape, ice crystal roughness, and the vertical distribution of impurities in the snow–atmosphere system, data that are critical for estimating snow albedo for use in climate models.
Drone CO2 measurements during the Tajogaite volcanic eruption
John Ericksen, Tobias P. Fischer, G. Matthew Fricke, Scott Nowicki, Nemesio M. Pérez, Pedro Hernández Pérez, Eleazar Padrón González, and Melanie E. Moses
Atmos. Meas. Tech., 17, 4725–4736, https://doi.org/10.5194/amt-17-4725-2024, 2024
Volcanic eruptions emit significant quantities of carbon dioxide (CO2) to the atmosphere. We present a new method for directly determining the CO2 emission from a volcanic eruption on the island of La Palma, Spain, using an unpiloted aerial vehicle (UAV). We also collected samples of the emitted CO2 and analyzed their isotopic composition. Together with the emission rate the isotopic data provide valuable information on the state of volcanic activity and the potential evolution of the eruption.
Impact and Optimization of Calibration Conditions for Air Quality Sensors in the Long-term Field Monitoring
Han Mei, Peng Wei, Meisam Ahmadi Ghadikolaei, Nirmal Kumar Gali, Ya Wang, and Zhi Ning
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-130,2024
Preprint under review for AMT (discussion: open, 0 comments)
Long-term field testing across diverse climatic environments is conducted to identify the optimized calibration conditions for NO2, NO, CO, and O3 electrochemical sensors. The results uncovered three factors that influence calibration performance: calibration period, concentration range, and time averaging. We developed a comprehensive framework for the best sensor calibration practices, which serves as a valuable reference for calibrating various sensor types used in air quality monitoring.
A large-scale validation of snowpack simulations in support of avalanche forecasting focusing on critical layers
Florian Herla, Pascal Haegeli, Simon Horton, and Patrick Mair
Nat. Hazards Earth Syst. Sci., 24, 2727–2756, https://doi.org/10.5194/nhess-24-2727-2024, 2024
Snowpack simulations are increasingly employed by avalanche warning services to inform about critical avalanche layers buried in the snowpack. However, validity concerns limit their operational value. We present methods that enable meaningful comparisons between snowpack simulations and regional assessments of avalanche forecasters to quantify the performance of the Canadian weather and snowpack model chain to represent thin critical avalanche layers on a large scale and in real time.
Abstract
Low Earth orbit (LEO) radio occultation|radio occultations (RO) constellations can provide global electron density profiles (EDPs) to better specify and forecast the ionosphere-thermosphere (I-T) system. To inform future RO constellation design, this study uses comprehensive Observing System Simulation Experiments (OSSEs) to assess the ionospheric specification impact of assimilating synthetic EDPs into a coupled I-T model. These OSSEs use 10 different sets of RO constellation configurations containing 6 or 12 LEO satellites with base orbit parameter combinations of 520 or 800 km altitude, and 24° or 72° inclination. The OSSEs are performed using the Ensemble Adjustment Kalman Filter implemented in the data assimilation (DA) Research Testbed and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). A different I-T model is used for the nature run, the Whole Atmosphere Model-Ionosphere Plasmasphere Electrodynamics (WAM-IPE), to simulate the period of interest is the St. Patrick's Day storm on March 13–18, 2015. Errors from models and EDP retrieval are realistically accounted for in this study through distinct I-T models and by retrieving synthetic EDPs through an extension Abel inversion algorithm. OSSE assessment, using multiple metrics, finds that greater EDP spatial coverage leading to improved specification at altitudes 300 km and above, with the 520 km altitude constellations performing best due to yielding the highest observation counts. A potential performance limit is suggested with two 6-satellite constellations. Lastly, close examination of Abel inversion error impacts highlights major EDP limitations at altitudes below 200 km and dayside equatorial regions with large horizontal gradients and low electron density magnitudes.
