Showing papers by "David F. Young published in 2004"

CERES cloud property retrievals from imagers on TRMM, Terra, and Aqua

Abstract: The micro- and macrophysical properties of clouds play a crucial role in Earth’s radiation budget The NASA Clouds and Earth’s Radiant Energy System (CERES) is providing simultaneous measurements of the radiation and cloud fields on a global basis to improve the understanding and modeling of the interaction between clouds and radiation at the top of the atmosphere, at the surface, and within the atmosphere Cl oud properties derived for CERES from the Moderate Resolution Imaging Spectrora diometer (MODIS) on the Terra and Aqua satellites are compared to ensure consistency between the products to ensure the reliability of the retrievals from multiple platforms at different times of day Comparisons of cloud fraction, height, optical depth, phase, effective particle size, and ice and liquid water paths from the two satellites show excellent consistency Initial calibration comparisons are also very favorable Differences between the Aqua and Terra results are generally due to diurnally dependent changes in the clouds Additional algorithm refinement is needed over the polar regions for Aqua and at night over those same areas for Terra The results should be extremely valuable for model validation and improvement and for improving our understanding of the relationship between clouds and the radiation budget keywords: radiation, clouds, remote sensing, cloud microphysics, climatology, MODIS, CERES, VIRS, Aqua, Terra

Application of deep convective cloud albedo observation to satellite-based study of the terrestrial atmosphere: monitoring the stability of spaceborne measurements and assessing absorption anomaly

Abstract: An objective method is developed to monitor the stability of spaceborne instruments, aimed at distinguishing climate trend from instrument drift in satellite-based climate observation records. This method is based on four-years of Clouds and the Earth's Radiant Energy System (CERES) broadband observations of deep convective cloud systems with cloud-top temperature lower than 205 K and with large optical depths. The implementation of this method to the CERES instrument stability analysis reveals that the monthly albedo distributions are practically the same for deep convective clouds with CERES measurements acquired from both the Tropical Rainfall Measuring Mission and Terra satellite platforms, indicating that CERES instruments are well calibrated and stable during both missions. Furthermore, with a nonlinear regression neural network narrowband-broadband conversion, this instrument-stability monitoring method can also be applied to narrowband instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Scanner (VIRS). The results show that the drifts associated with both VIRS and MODIS instruments are less than 1% during a four-year period. Since the CERES albedo measurements are highly accurate, the absorptance of these opaque clouds can be reliably estimated. The absorptions of these clouds from observations are around 25%, whereas the absorptions from theory can be as low as 18%, depending on ice cloud microphysics.

Real-Time Cloud, Radiation, and Aircraft Icing Parameters from GOES over the USA

Abstract: A preliminary new, physically based method for realtime estimation of the probability of icing conditions has been demonstrated using merged GOES-10 and 12 data over the continental United States and southern Canada. The algorithm produces pixel-level cloud and radiation properties as well as an estimate of icing probability with an associated intensity rating Because icing depends on so many different variables, such as aircraft size or air speed, it is not possible to achieve 100% success with this or any other type of approach. This initial algorithm, however, shows great promise for diagnosing aircraft icing and putting it at the correct altitude within 0.5 km most of the time. Much additional research must be completed before it can serve as a reliable input for the operational CIP. The delineation of the icing layer vertical boundaries will need to be improved using either the RUC or balloon soundings or ceilometer data to adjust the cloud base height, a change that would require adjustment of the cloud-top altitude also.

Diurnal, Seasonal, and Interannual Variations of Cloud Properties Derived for CERES From Imager Data

Abstract: Simultaneous measurement of the radiation and cloud fields on a global basis is a key component in the effort to understand and model the interaction between clouds and radiation at the top of the atmosphere, at the surface, and within the atmosphere. The NASA Clouds and Earth s Radiant Energy System (CERES) Project, begun in 1998, is meeting this need. Broadband shortwave (SW) and longwave radiance measurements taken by the CERES scanners at resolutions between 10 and 20 km on the Tropical Rainfall Measuring Mission (TRMM), Terra, and Aqua satellites are matched to simultaneous retrievals of cloud height, phase, particle size, water path, and optical depth OD from the TRMM Visible Infrared Scanner (VIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua. Besides aiding the interpretation of the broadband radiances, the CERES cloud properties are valuable for understanding cloud variations at a variety of scales. In this paper, the resulting CERES cloud data taken to date are averaged at several temporal scales to examine the temporal and spatial variability of the cloud properties on a global scale at a 1 resolution.

Investment in education: the implications for economic growth and public finances - Andrea Montanino, Bartosz Przywara and David Young

Abstract: This paper analyses the demographic and institutional influences underlying public spending on education, as well as the consequences for average educational attainment and economic growth. The issues are topical given, on one hand, EU objectives for increased investment in human resources and, on the other, increasing concerns about the sustainability of public finances, particularly in view of ageing populations. The paper presents methodologies for projecting educational attainment and public expenditure on education. Tentative numerical results suggest that the growth of average educational attainment is likely to slow slightly, compared to recent decades. Nevertheless, education is set to continue making a substantial contribution to economic growth in the EU as a whole, though the impact varies widely among Member States. As regards public expenditure, although demographic trends mean a reduction in the potential number of students, this is offset by two factors: increasing enrolment rates at upper-secondary and tertiary level (projected taking into consideration either past developments in enrolment or the expected future evolution of labour force); and increasing expenditure per student (projected on the basis of recent trends). Thus, few savings - if any - are expected from reductions in expenditure on education due to changes in the demographic structure.

Students as Ground Observers for Satellite Cloud Retrieval Validation

Abstract: The Students' Cloud Observations On-Line (S'COOL) Project was initiated in 1997 to obtain student observations of clouds coinciding with the overpass of the Clouds and the Earth's Radiant Energy System (CERES) instruments on NASA's Earth Observing System satellites. Over the past seven years we have accumulated more than 9,000 cases worldwide where student observations are available within 15 minutes of a CERES observation. This paper reports on comparisons between the student and satellite data as one facet of the validation of the CERES cloud retrievals. Available comparisons include cloud cover, cloud height, cloud layering, and cloud visual opacity. The large volume of comparisons allows some assessment of the impact of surface cover, such as snow and ice, reported by the students. The S'COOL observation database, accessible via the Internet at http://scool.larc.nasa.gov, contains over 32,000 student observations and is growing by over 700 observations each month. Some of these observations may be useful for assessment of other satellite cloud products. In particular, some observing sites have been making hourly observations of clouds during the school day to learn about the diurnal cycle of cloudiness.

An Examination of the Impact of Drizzle Drops on Satellite-Retrieved Effective Particle Sizes

Abstract: In general, cloud effective droplet radii are remotely sensed in the near-infrared using the assumption of a monomodal droplet size distribution. It has been observed in many instances, especially in relatively pristine marine environments, that cloud effective droplet radii derived from satellite data often exceed 15 m or more. Comparisons of remotely sensed and in situ retrievals indicate that the former often overestimates the latter in clouds with drizzle-size droplets. To gain a better understanding of this discrepancy, this paper performs a theoretical and empirical evaluation of the impact of drizzle drops on the derived effective radius.

Comparison of cloud properties from meteosat-8 and surface observations

Abstract: A set of algorithms used to derive cloud properties globally has been adapted to analyze hourly radiances taken by Meteosat-8. The initial results are evaluated using objective surface observations at several European locations. Cloud amounts appear to be underestimated due to the satellite retrievals missing some optically thin clouds. False cloud detections occur along arid coastlines and for heavy aerosols. Improvement in cloud detection awaits refinements of the algorithms for the SEVIRI channels and in the clear-sky radiances used to discriminate cloudy and clear scenes. Cloud-top heights are in good agreement for liquid and optically thick ice clouds but are underestimated for optically thin ice clouds. Further enhancement of the algorithms is underway.

An Improved Radiation Budget Data Set Using Merged CERES and GEO Data

Abstract: Long term radiation budget datasets are needed to monitor the Earth’s climate. The Clouds in the Earth’s Radiant Energy System (CERES) experiment provides the most accurate observations of the Earth’s global energy budget to date. Instantaneous accurate fluxes need to be globally temporally and spatially averaged to become useful in climate monitoring. Unfortunately satellite based measurements can have temporal sampling biases due to orbital constraints. CERES incorporates radiances from imagers aboard geostationary (GEO) satellites to determine changes in meteorology between CERES sampling times. The geostationary radiances need to be accurately calibrated, converted to broadband radiances to take into account the radiation not observed by the narrowband spectra, temporally interpolated and carefully normalized to the CERES measurements. This paper describes this process and demonstrates the reduction in temporal sampling errors from the inclusion of the GEO data.

Lessons Learned in CERES: Integrating Multiple Instruments on Multiple Platforms with Multiple Sources of Data

Abstract: This paper discussed the complex issues in com bining remote sensing data from a variety of sources into a unified set of data products that can be used in the analysis of climate change. Creation of climate quality data records from remote sensing observations presents special challenges to the scien ce data processing segment of an instrument team. Throughout its history, remote sensing systems have recognized instrument calibration adjustments over time as necessary. Long -term stability over many decades is a unique climate data requirement imposed on remotely sensed data and creates special problems when information technology is rapidly evolving. Over the life of an observational data set, changes in ground processing environments, if not handled correctly, can create unexpected biases in signals and are a special challenge when the hardware, operating systems and processing libraries change on a quarterly basis. Planning for ground processing systems to support climate data records must incorporate requirements for accommodating changes to the t echnology and provide for a means of validating the stability of data products. This planning becomes particularly useful when the observational system lifetime extends through several lifetimes of the ground processing systems, and yet requires the elimi nation of errors created by changing the technologies in science data processing.