Evaluation of the performances of two rebs net radiometer designs during Nimex at a tropical site in Ile-Ife, Nigeria (original) (raw)
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Estimating net radiation using routine meteorological data at a tropical location in Nigeria
International Journal of Sustainable Energy, 2006
Ground heat flux (G o) plays an important role in the partitioning of energy budget at earth's surface. The estimates of G 0 are required as part of boundary conditions by all general circulation models. In this work, reliability of four simple and computationally cheap models was tested against a more complex and reliable model as the reference. The simple models selected for investigation are: Simple measurement (SM), Percentage of net radiation (PR), Universal function of net radiation (UR), and Linear function of net radiation (LR) models. Force restore model (FR) was used as the reference model. The data of soil temperature measured at the surface and 0.05 m depth, soil heat flux, measured at 0.05m, and net radiation were obtained from Nigerian Micrometeorological Experiment, Ile Ife. Force restore model was first calibrated with direct measurements for soil heat flux at 0.05 m depth with satisfactory result before it was employed to generate reference G 0 estimates. Estimates of SM, PR, UR and LR were compared with FR using simple statistics of coefficient of determination (R 2), slope, intercept, root mean square error (RMSE) and mean bias error (MBE). The SM model reproduced the daytime and night-time variations of G 0 better than all the models that parameterized G 0 as a function of net radiation (R 2 , slope, intercept, RMSE and MBE values of 0.85, 0.87, 3.43W/m 2 , 32.69, W/m 2 ,-3.70 W/m 2 respectively). This model however requires measurement of both soil heat flux and temperature. The LR model generated the best estimates of G o out of all the models that utilized net radiation measurements (R 2 , slope, intercept, RMSE and MBE values are 0.60, 0.58,4.55 W/m 2 , 53.81 W/m 2 and 3.60 W/m 2 respectively) while UR model is the worst. The LR model, though depend only on one measurement, requires site-specific calibrations and can therefore be deployed for gap filling where SM model cannot be used
Evaluation of measurement accuracy and comparison of two new and three traditional net radiometers
Agricultural and Forest Meteorology, 2009
Net radiation (R n ) is the sum of the radiant energy at the Earth's surface and is a major component of the surface energy balance. However, R n is difficult to measure accurately, and multiple instruments are available to measure it. Two new instruments (Hukseflux Thermal Sensors B.V., model NR01; Kipp & Zonen B.V., model CNR 2) have been released within the past two years. We compared these models, two less-expensive older models (Kipp & Zonen B.V., model NR-Lite; Radiation and Energy Balance Systems, Inc., model Q*7.1), and a more expensive older model (Kipp & Zonen B.V., model CNR 1) over a uniform turfgrass surface for 33 days in mid-summer. Three replicates of each radiometer were included in the study (except for the CNR 1). The instruments that independently measure the four components of R n (models CNR 1 and NR01) were typically the most accurate. Incoming shortwave measurements from the four component instruments were compared to a reference pyranometer, and outgoing longwave measurements were compared to infrared measurements of surface temperature. The differences from the reference pyranometer and surface temperature measurements were typically 2% or less. There was a difference of approximately 5% in incoming longwave measurements between these two radiometer models. This is likely due to differences in calibration approaches, which are discussed. This emphasizes the need for standardization of longwave calibration methods and establishment of a world reference for longwave radiation. The instruments that do not separate shortwave and longwave radiation into component measurements (net all-wave radiometers, models NR-Lite and Q*7.1) were generally the least accurate, and had offsetting day and night differences that reduced daily total R n differences relative to the reference. The CNR 2 measures net shortwave and net longwave, and is an intermediate between a four component instrument and a net all-wave instrument. The R n measurement accuracy of the CNR 2 typically fell between that of the two groups. Differences among radiometers tended to be larger at night than during the day, indicating higher variability in longwave measurements. An inversion (flip) test in the field showed the NR-Lites and Q*7.1s had well matched detectors, however two of the three replicate CNR 2s had mismatch errors greater than 5%. This becomes important for measurements over nonvegetated surfaces. The data presented here should be helpful in selecting the most cost effective instrument for a given application. ß
This paper examines the distribution of the surface radiation balance components measured during the Nigerian Micrometeorological Experiment (NIMEX-1), a field study conducted to measure surface heat fluxes in the boundary layer during the transition period which marks the end of dry season and the onset of wet season (February 15 and March 10, 2004) in the southwestern part of Nigeria. Regression equations were obtained using the daily average values and hourly mean values between net shortwave and net longwave radiation, respectively, with the global radiation. Higher correlations with low standard error of measurement were obtained for daily mean values than the hourly mean. It was also observed that the peak values of each type of radiation during the period occurred, on average, two hours after noon when it was expected to occur.
Engenharia Agrícola, 2014
Radiation balance is the fraction of incident solar radiation upon earth surface which is available to be used in several natural processes, such as biological metabolism, water loss by vegetated surfaces, variation of temperature in farming systems and organic decomposition. The present study aimed to assess and validate the performance of two estimation models for Rn in Ponta Grossa city, Paraná State, Brazil. To this end, during the period of 04/01/2008 to 04/30/2011, from radiometric data collected by an automatic weather station set at the Experimental Station, of the State University of Ponta Grossa. We performed a linear regression study by confrontation between measurements made through radiometric balance and Rn estimates obtained from Brunt classical method, and the proposed method. Both models showed excellent performance and were confirmed by the statistical parameters applied. However, the alternative method has the advantage of requiring only global solar radiation val...
Journal of Atmospheric and Oceanic Technology, 2000
The Kipp & Zonen NR-Lite is a newly designed domeless net radiometer. In preparation for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project, the NR-Lite was rigorously field tested for over eight months during 1998. Seven NR-Lites were compared to an Eppley four-component PSP/PIR net radiometer system, a Kipp & Zonen four-component CNR1, and a REBS Q*7.1. Measurement problems associated with calibration, precipitation, cosine response, and wind-induced error were examined. Results conclude that the NR-Lite is well-suited for experiments where remote, long-term measurements of net radiation are required.
Validation of ground-based microwave radiometer measurements over a tropical coastal station
2019 URSI Asia-Pacific Radio Science Conference (AP-RASC), 2019
Ground-based, passive, multi-frequency microwave radiometer profilers (MRP) are very powerful tools to provide vertical profiles of atmospheric parameters under almost all-weather conditions. However, these retrievals are to be validated through other independent estimates, before these are used for scientific studies. Such a validation exercise has been carried out for the MRP, operational at the tropical coastal station, Thiruvananthapuram (TVM), which has been in regular operation since 2010. The validation is done through the inter-comparison of the MRP measured brightness temperature (Tmathrmb)( T_{\mathrm{b}})(Tmathrmb) with those simulated using microwave radiative transfer scheme that uses collocated and concurrent profiles of temperature and humidity from radiosonde. The analyses have shown a very good correlation (sim0.9)( \sim 0.9)(sim0.9) with 0.5 K bias for V-band frequency channels while for the K-band frequency channels a 3–5 K bias is seen due to the variability in the water vapour content. The dir...
This study is comprised of two parts. The first part provides the long-term mean annual cycle context for the deployment of Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) in Niamey, Niger, Africa, during the entire year of 2006. Documentation includes the annual cycles (calendar month basis) of the following surface meteorological variables that will be important for the ARM deployment-rainfall, visibility (proxy for atmospheric dust), vapor pressure (proxy for column precipitable water), daily maximum and minimum temperature, dew point temperature, and relative humidity. These annual cycles illustrate the strong control of rainfall on the other surface parameters. This theme is further developed in the second part of the poster that presents the annual cycles of the same parameters for the highly contrasting years of 2004 (moderately dry) and 2005 (moderately wet). The 2005 wetness likely reduced the effects of atmospheric dust on the AMF measurements made in Niamey in the early months of 2006.
Evaluation of net radiation using the autoregressive models with higher orders over Nigeria
Journal of Advances in Science and Engineering, 2020
Net radiation is the amount of the difference between upward and downward components of long wave and shortwave radiation; a central component of the Earth's equilibrium surface energy. It is the primary source of energy for the physical and chemical processes, which occur in the surfaceatmosphere interface [1]. It has served as an input parameter for the global modeling of hydrological budgets, photosynthesis, and evapotranspiration [2]. The near energy balance and precision of evapotranspiration estimation algorithms are especially affected by the net radiation [3]. For meteorology, hydrology, global change and agriculture, the accurate estimate of net radiation is critical [4]-[6]. While net radiometer can measure net radiation in a station accurately, its use is complex and time consuming for large-scale
Measurements of net all-wave radiation at a tropical location, Ile-Ife, Nigeria
Atmósfera, 2014
Se presentan datos de radiación neta en todas las longitudes de onda promediados cada hora, registrados en una estación meteorológica situada en el campus de la Universidad Obafemi Awolowo, Ile-Ife (7.52º N, 4.52º E), Nigeria, durante un periodo completo de tres años (2010-2012), para estudiar sus variaciones diurnas y estacionales. Esta información, obtenida con un radiómetro neto de alta sensibilidad de cuatro componentes, representa hasta hoy la información más consistente y detallada disponible para una localidad tropical de África Occidental. De acuerdo con los datos obtenidos, la radiación neta máxima ocurrió a las 14:00 LT (GMT + 1), y sus valores se incrementaron de manera considerable de 337.6 ± 146.4 Wm-2 en julio, que es el pico de la estación lluviosa, a 441.7 ± 82.4 Wm-2 durante marzo, en el final de la estación seca. En los meses de abril y octubre, que marcan el principio y fin de la estación lluviosa en Ile-Ife, se han registrado los valores más altos de radiación neta: 584.7 y 612.2 Wm-2 , respectivamente. Se observó una importante variación inter e intraestacional en los valores medios mensuales de radiación neta, debida principalmente a fluctuaciones de nubosidad y humedad. En el área de estudio, los datos revelaron la presencia de calentamiento radiativo neto en la superficie, cuya tendencia anual sigue una distribución bimodal. Los datos de este estudio respaldan los aportados por otros autores.
Journal of Rock Mechanics and Geotechnical Engineering, 2017
When modeling the soil/atmosphere interaction, it is of paramount importance to determine the net radiation flux. There are two common calculation methods for this purpose. Method 1 relies on use of air temperature, while Method 2 relies on use of both air and soil temperatures. Nowadays, there has been no consensus on the application of these two methods. In this study, the half-hourly data of solar radiation recorded at an experimental embankment are used to calculate the net radiation and long-wave radiation at different time-scales (half-hourly, hourly, and daily) using the two methods. The results show that, compared with Method 2 which has been widely adopted in agronomical, geotechnical and geo-environmental applications, Method 1 is more feasible for its simplicity and accuracy at shorter time-scale. Moreover, in case of longer time-scale, daily for instance, less variations of net radiation and long-wave radiation are obtained, suggesting that no detailed soil temperature variations can be obtained. In other words, shorter time-scales are preferred in determining net radiation flux.