Papers by John Le Marshall
Vertical Atmospheric Structures Associated with Positive Biases in COSMIC-2 Refractivity Retrievals
Journal of Atmospheric and Oceanic Technology
Representation of complex vertical structures observed in the troposphere can vary depending on d... more Representation of complex vertical structures observed in the troposphere can vary depending on data sources. The radio occultation (RO) technique offers great advantages for sensing the atmosphere down to its lowermost layers using high-resolution measurements collected by satellites on low-Earth orbit (LEO). The structures are generally smoother in vertical when reproduced from atmospheric models. We evaluate the quality of troposphere retrievals from the COSMIC-2 mission and demonstrate that systematic effects in fractional refractivity deviations with respect to European Centre for Medium-Range Weather Forecasts (ECMWF) background fields are spatially correlated with positive refractivity gradients characterized as subrefraction. The magnitude of refractivity biases observed mostly over the equatorial regions can exceed 1% within altitudes of 3–5 km. Respective zonal means reveal seasonal trends linked with the distribution of atmospheric inversion layers and signal-to-noise rat...
Simulations of GPS Radio Occultation Signal Paths
Earth Observation from Space - Recent Advances
Earth observations from space (EOS), taken by advanced instruments on current and planned satelli... more Earth observations from space (EOS), taken by advanced instruments on current and planned satellite missions will increasingly provide large volumes of data related to the atmospheric, oceanic, and land surface state. We describe some key benefits to Australia from these Earth observations. Many of the benefits described are in the atmospheric, oceanographic or climate areas. Instruments providing these benefits include the Atmospheric Infrared Sounder, those carried by the COSMIC Constellation and the MTSAT imager. Examples of the beneficial impact of these data over the Australian region and southern hemisphere are provided. Many examples are Observing System Experiments, based on the application of these data to the operational forecast system of the Australian Bureau of Meteorology. It is found in an era where populations are increasing in areas subjected to severe weather and while extreme weather events remain a considerable problem, that for example over the southern hemisphe...
Recent and Impending Advances in the Use of Earth Observations from Space for Numerical Weather Prediction
Australian Space Research Program—Platform Technologies for Space, Atmosphere and Climate Project: Selected Innovations
Mathematics for Industry, 2015
In 2010 an international consortium led by RMIT University was awarded a multi-million-dollar Aus... more In 2010 an international consortium led by RMIT University was awarded a multi-million-dollar Australian Space Research Program (ASRP) Project—“Platform Technologies for Space Atmosphere and Climate”. This project is part of the Australian Government’s recent space-related initiative to support national strategic, economic and social objectives. The aim of the project was to develop new algorithms, new approaches, software and system platforms for enhancing Australias capability in space-related research and promoting innovative applications of space-related cutting-edge technologies in Australia. The main project objectives and a selection of innovative research findings are presented, highlighting the applications, practical conceptualization and mathematics required.
Limb Effects in Satellite Temperature Sounding
Journal of Climate and Applied Meteorology, 1985
Abstract To date, operational satellite temperature retrieves from the TIROS-N/NOAA A–G series of... more Abstract To date, operational satellite temperature retrieves from the TIROS-N/NOAA A–G series of satellites and a large percentage of those produced for research purposes have used statistical techniques to estimate limb effects in satellite-observed radiances. In this study, temperature profiles were derived using the radiative transfer equation in a form which properly takes into account the angle of observation. These temperature profiles were then compared to those derived using the radiative transfer equation with “nadir radiances” produced by a statistical limb correction technique similar to those now used operationally. This comparison revealed significant differences in the derived temperature profiles at large viewing angles, particularly in the case of strong meridional temperature gradients. Overall, the results suggest that for the calculation of temperature profiles from nonnadir observations, the more proper physical solution is the preferred procedure for deriving temperature fields.
It has long been hypothesised that arid areas such as the Simpson Desert would make an ideal grou... more It has long been hypothesised that arid areas such as the Simpson Desert would make an ideal ground calibration target for passive microwave missions, due to their supposed temporally and spatially consistent microwave emission characteristics. With the imminent launch of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission, it is important to answer this question now so that such targets can be included in the planning for initial post-launch calibration activities. A recent airborne campaign to the Australian arid zone has assessed i) the Simpson Desert, ii) Lake Eyre and iii) some gibber plains for this purpose. SMOS sized pixels of approximately 50x50km have been mapped in entirety at 1km resolution during the scheduled 6am SMOS overpass time, using thermal infrared sensors and the Polarimetric L-band Multibeam Radiometer (PLMR) which operates at the same frequency as SMOS. Such observations were supplemented by high resolution (50m) PLMR measurements...
Weather and Forecasting, 2008
Extended-length observing system experiments (OSEs) during two seasons are used to quantify the c... more Extended-length observing system experiments (OSEs) during two seasons are used to quantify the contributions made to forecast quality by conventional rawinsonde data and four types of remotely sensed satellite data. The impact is measured by comparing the analysis and forecast results from an assimilation–forecast system using all data types with those excluding a particular observing system. The impact of the particular observing system is assessed by comparing the forecast results over extended periods. For these observing system experiments, forecast results are compared through 168 h for periods covering more than a month during both the summer and winter seasons of each hemisphere. The assimilation–forecast system used for these experiments is the National Centers for Environmental Prediction (NCEP) Global Data Assimilation System (GDAS) and the Global Forecast System (GFS). The case studies chosen consist of periods during January–February 2003 and August–September 2003. Duri...
Weather and Forecasting, 2010
A two-season observing system experiment (OSE) was used to quantify the impacts of assimilating t... more A two-season observing system experiment (OSE) was used to quantify the impacts of assimilating the WindSat surface winds product developed by the Naval Research Laboratory (NRL). The impacts of assimilating these surface winds were assessed by comparing the forecast results through 168 h for the months of October 2006 and March 2007. The National Centers for Environmental Prediction’s (NCEP) Global Data Assimilation/Global Forecast System (GDAS/GFS) was used, at a resolution of T382-64 layers, as the assimilation system and forecast model for these experiments. A control simulation utilizing all the data types assimilated in the operational GDAS was compared to an experimental simulation that added the WindSat surface winds. Quality control procedures required to assimilate the surface winds are discussed. Anomaly correlations (ACs) of geopotential heights at 1000 and 500 hPa were evaluated for the control and experiment during both seasons. The geographical distribution of the for...
The Joint Center for Satellite Data Assimilation (JCSDA) was established by NASA and NOAA in 2001... more The Joint Center for Satellite Data Assimilation (JCSDA) was established by NASA and NOAA in 2001, with the DoD becoming a partner in 2002. The goal of the JCSDA is to accelerate the use of observations from earth-orbiting satellites in operational numerical analysis and prediction models for the purpose of improving weather forecasts, improving seasonal to interannual climate forecasts, and increasing the accuracy of climate data sets. Advanced instruments of the current and planned satellite missions, do and will increasingly provide large volumes of data related to atmospheric, oceanic, and land surface state. These data will exhibit accuracies and spatial, spectral and temporal resolutions never before achieved. The JCSDA will ensure that the maximum benefit from investment in space is realised from the advanced global observing system. It will also help accelerate the use of satellite data from both operational and experimental spacecraft for weather and climate related activities. To this end the advancement of data assimilation science by JCSDA has included the establishment of the JCSDA Community Radiative Transfer Model (CRTM) and continual upgrades including, the incorporation of AIRS and snow and ice emissivity models for improving the use of microwave sounding data over high latitudes, preparation for use of METOP IASI/AMSU/HSB, DMSP SSMIS and CHAMP GPS data, real-time delivery of EOS-Aqua AMSR-E to NWP centers, and improved physically based SST analyses. Eighteen other research projects are also being supported by the JCSDA (e.g. use of cloudy radiances from advanced satellite instruments) to develop a state of-the-art satellite data assimilation system. The work undertaken by the JCSDA represents a key component of GEOSS. In particular data assimilation, data impact studies, OSSEs, THORPEX and network design studies are key activities of GEOSS. Recent advances at the JCSDA including the demonstration of the benefits in the Northern and Southern Hemisphere of AIRS radiance assimilation on NCEP GFS forecasts, demonstration of the benefits of MODIS Polar atmospheric motion vector assimilation on NCEP GFS forecasts and the beneficial impact of the CRTM's modeling of sea ice and snow emissivity are recorded below.
Bulletin of the American Meteorological Society, 1985
The utility of VISSR Atmospheric Sounder (VAS) temperature and moisture soundings and cloud and w... more The utility of VISSR Atmospheric Sounder (VAS) temperature and moisture soundings and cloud and water vapor motion winds in defining a storm and its surroundings at subsynoptic scales has been examined using a numerical analysis and prognosis system. It is shown that the VAS temperature and moisture data, which specify temperature and moisture well in cloud-free areas, are complemented by cloud and water vapor motion data generated in the cloudy areas. The cloud and water vapor "winds" provide thermal gradient information for interpolating the soundings across cloudy regions. The loss of analysis integrity due to the reduction of VAS sounding density in the cloudy regions associated with synoptic activity is ameliorated by using cloud and water vapor motion winds. The improvement in numerical forecasts resulting from the addition of these data to the numerical analysis is recorded.
IEEE Transactions on Geoscience and Remote Sensing, 2014
The Soil Moisture and Ocean Salinity (SMOS) satellite marks the commencement of dedicated global ... more The Soil Moisture and Ocean Salinity (SMOS) satellite marks the commencement of dedicated global surface soil moisture missions, and the first mission to make passive microwave observations at L-band. On-orbit calibration is an essential part of the instrument calibration strategy, but on-board beam-filling targets are not practical for such large apertures. Therefore, areas to serve as vicarious calibration targets need to be identified. Such sites can only be identified through field experiments including both in situ and airborne measurements. For this purpose, two field experiments were performed in central Australia. Three areas are studied as follows: 1) Lake Eyre, a typically dry salt lake; 2) Wirrangula Hill, with sparse vegetation and a dense cover of surface rock; and 3) Simpson Desert, characterized by dry sand dunes. Of those sites, only Wirrangula Hill and the Simpson Desert are found to be potentially suitable targets, as they have a spatial variation in brightness temperatures of < 4 K under normal conditions. However, some limitations are observed for the Simpson Desert, where a bias of 15 K in vertical and 20 K in horizontal polarization exists between model predictions and observations, suggesting a lack of understanding of the underlying physics in this environment. Subsequent comparison with model predictions indicates a SMOS bias of 5 K in vertical and 11 K in horizontal polarization, and an unbiased root mean square difference of 10 K in both polarizations for Wirrangula Hill. Most importantly, the SMOS observations show that the brightness temperature evolution is dominated by regular seasonal patterns and that precipitation events have only little impact.
The Japanese Meteorological Agency (JMA) launched the geostationary satellite Himawari-8 in Octob... more The Japanese Meteorological Agency (JMA) launched the geostationary satellite Himawari-8 in October 2014. The satellite provides 10 minute, sixteen band imagery over the Asian and Australasian region. The imagery has been navigated, calibrated and subsequently used in the Bureau of Meteorology (BoM) to generate Atmospheric Motion Vectors (AMVs) over the full earth disk viewed from the satellite every ten minutes. Each vector has been error characterised and assigned an expected error. In preparation for the operational assimilation of the 10-minute data, these high temporal and spatial resolution data were used in the BoM test operational database to provide forecasts from the next generation operational forecast model ACCESS APS2 using 4D Var. Results from these tests indicate these locally generated Himawari-8 10 minute AMVs are of high quality and density and have the potential to improve numerical weather prediction (NWP) model initialisation and forecasts. The forecasts underta...
An Analysis Of The Impact Of Earth Observations From Space On Australian And Global Numerical Weather Prediction
An Analysis Of The Impact Of Earth Observations From Space On Australian And Global Numerical Wea... more An Analysis Of The Impact Of Earth Observations From Space On Australian And Global Numerical Weather Prediction. John Le Marshall(1,3), Jin Lee(1), Paul Gregory(1) Jim Jung(2), Robert Norman(3), and Rolf Seecamp(1). (1) Bureau of Meteorology, Australia, (2) Joint Center for Satellite Data Assimilation, USA, (3) RMIT University, Melbourne, Australia Earth observations from space (EOS), taken by advanced instruments on current and future satellite missions will increasingly provide large volumes of data related to Earth System State. Key benefits from assimilating these earth observations, particularly from an Australian Region and southern hemisphere perspective have been documented. The benefits described are in relation to synoptic scale and severe weather forecasts. Instruments providing these benefits include the Atmospheric Infrared Sounder, those carried by the COSMIC Constellation and the GOES and MTSAT imager. Examples of the beneficial impact of these data are provided. Man...
Bureau Research Report, 2016
The Bureau of Meteorology advise that the information contained in this publication comprises gen... more The Bureau of Meteorology advise that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law and the Bureau of Meteorology (including each of its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.
Journal of Southern Hemisphere Earth System Science, 2017
The beneficial impact of radio occultation observations on Australian region forecasts
Australian Meteorological and Oceanographic Journal, 2010
Impact of METOP ASCAT Ocean Surface Winds on Global Weather Forecasts
High Spatial and Temporal Resolution Atmospheric Motion Vectors – Generation, Error Characterization and Assimilation
Data from the Japanese geostationary satellite MTSAT -1R (and at times MTSAT-2) have been receive... more Data from the Japanese geostationary satellite MTSAT -1R (and at times MTSAT-2) have been received at the Bureau of Meteorology (BoM) satellite groundstation at Crib Point, Victoria. Calibrated and navigated sequential radiance data have been subsequently used to calculate high density Atmospheric Motion Vectors (AMVs). These AMVs have been generated almost continuously throughout the day using sequential images separated by 15-minutes, 30 minutes or an hour. The winds have been calculated using infrared (11 µm), (high resolution) visible (0.5 µm) and water vapour absorption (6.7 µm) band images. The AMVs have been error characterized with error characteristics including the correlated error, the length scale of the correlated error, the Expected Error and Quality Indicator being estimated. These AMV data are important for operational NWP, research and particularly for severe weather forecasting, including tropical cyclone track forecasting. The data have been used in real time data...
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Papers by John Le Marshall