Photosynthetically Active Radiation Values Research Articles

Influence of photosynthetic active radiation on sap flow dynamics across forest succession stages in Dinghushan subtropical forest ecosystem

With the intensification of global change, forests are subjected to varying degrees of drought or high-temperature stress, which has an indelible impact on the growth of trees. However, knowledge on the response of sap flow to environmental changes in different types of forests is still rare, especially in China's subtropical forest ecosystem. Consequently, studying how different tree species regulate their sap flow in response to shifting environmental conditions is essential for understanding forest transpiration, water use efficiency, and drought stress resilience. Therefore, this study aimed to investigate the sap flow dynamics of seven tree species in five forest plots, i.e., pine forest (PF), two types of mixed conifer-broadleaf forests (MF1+MF2), monsoon evergreen broadleaved forest (MEBF), and montane monsoonal evergreen broad-leaf forest (MOBF) at Dinghushan National Reserve in Southern China, using the heat dissipation probe technique and synchronous environmental factor recordings. Results demonstrated a significant influence of photosynthetic active radiation (PAR) on sap flow across all tree species, with mean PAR values ranging from over 1200 to 425 μmol m−2 s−1, establishing it as the principal driving factor. This observation underscores the heightened responsiveness or sensitivity of tree species to variations in PAR as the forest undergoes development and maturation. The correlation between vapor pressure deficit (VPD) and tree sap flow decreased as succession progressed. Moreover, the influence of soil water content (SWC) on sap flow stability against environmental changes increased. Similar patterns were also found between the two MF, with MF-2 displaying ecological characteristics and environmental conditions more closely aligned with those of the late-successional MEBF. The study reveals the intricate relationship between environmental factors and sap flow regulation in tree species within a subtropical forest ecosystem. Addressing a comparative gap in sap flow correlation among dominant tree species at Dinghushan, it establishes a hydro-physiological foundation for understanding tree species substitution during forest succession. The results provide key insights for forest management and climate-related research. Future studies should delve into the long-term implications of observed sap flow dynamics, exploring their impact on tree species adaptability amid ongoing environmental changes.

Estimation and Investigation of Photosynthetically Active Radiation Using Meteorological Parameters over Ikeja, Nigeria

Photosynthetically active radiation (PAR; 0.4 - 0.7μm) is a key driver in ecosystem biochemical processes, and thus a critical factor in agriculture productivity, ecosystem-atmosphere energy, and CO2 fluxes. In this study, the measured monthly averaged daily global solar radiation, relative humidity, wind speed, minimum and maximum temperature dataset was utilized to estimate and investigate the Photosynthetically Active Radiation (PAR) for Ikeja (latitude 6.58 N, longitude 3.33 E and 39.4 m above sea level) located in the coastal region ofNigeria. The meteorological parameters used in this work were obtained from the archives of National Aeronautics and space Administration (NASA) for a period of thirty-eight years (1984-2021).The newly developed temperature PAR based models were statistically tested using the coefficient of determination (R2), Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE), t – test and index of Agreement (IA) to ascertain the accuracy and applicability of the models. The results show that, the highest and lowest values of PAR were found during the rainy season with 8.3426 MJ and 6.4936 MJ in the months of April and July respectively. Based on the developed models, the model equation (16g) is the most suitable for estimating PAR for Ikeja with R2, MBE, RMSE, MPE, t-test and IA values of 80.9 , 0.0062 MJ , 0.3415 MJ -0.1974 0.0601 and 92.8712 respectively.

Monthly intercepted photosynthetically active radiation estimation based on the Beer-Lambert’s law across the cereal crops of Castilla y León (Spain)

Agriculture is by far the most important economic activity in the Spanish autonomous region of Castilla y León. Numerous factors influence crop development but one of the most related variables to the photosynthetic process is Photosynthetically Active Radiation (PAR). Estimating Intercepted Photosynthetically Active Radiation (IPAR) in different crops through the Beer-Lambert law could be a relevant factor in crop season planning by enabling photosynthesis monitoring. The Beer-Lambert Law is applied in this study to the data for almost 2 million hectares of wheat, barley, and maize cultivated in Castilla y León in 2021. The fourteen-year data set of Global Horizontal Irradiance (GHI) used to calculate the monthly PAR data in the region was collected at 93 meteorological stations (46 in Castilla y León and 47 in neighboring Spanish and Portuguese regions). Two previously published global calibrated models were employed to calculate the PAR, with a relative Root Mean Square Error (rRMSE) below 6%, for the measured daily mean values of PAR in Burgos. Processing the various NASA Terra and Aqua satellite images yielded the monthly Leaf Area Index (LAI) and the literature review provided the light extinction coefficient (k). The Geographic Information System (GIS) facilitated visualization of IPAR estimates for the three cereal crops in all months of its growing season. Wheat and barley reach their IPAR peaks in June and July, while maize peaks in July and August. In addition, the fraction of Intercepted Photosynthetically Active Radiation (fIPAR) was calculated in different provinces to assess PAR interception for each cereal at different growing stages. In June, almost 50% of the wheat area in Burgos, Palencia and Soria displayed fIPAR values exceeding 45% while in the case of barley only the province of Burgos reached these percentages of area and.fIPAR.

Studying Conditions of Intense Harmful Algal Blooms Based on Long-Term Satellite Data

Harmful algal blooms (HABs) adversely impact aquatic organisms, human health, and the marine economy. The need to understand the origins and mechanisms of HAB occurrence and development determines the relevance of the study of these phenomena, including using remote sensing methods and assets. Here we present the results of a comprehensive study of conditions and precursors of some intense HABs detected in the water areas near the island of Chiloe (Chile, 2016), near the Kamchatka Peninsula (Russia, 2020), near the island of Hokkaido (Japan, 2021), among others. The study involves statistical analysis of long-term satellite and model data arrays on significant parameters of the marine environment and near-surface atmosphere, as well as empirical modeling of HAB risks. Information products on the following environmental parameters were used: sea surface temperature (SST, NOAA OISST, since 1981), the level of photosynthetically active radiation (PAR) and chlorophyll-a concentration (MODIS Ocean Color SMI, since 2000), sea surface salinity and height (HYCOM, since 1993), and near-surface wind speed and direction (NCEP CFSv2, since 1979). Quantitative assessments of the dynamics of informative criteria were applied. The key criterion is the ratio (Δσ) of the absolute deviation of the studied parameter from the expected norm to the RMS deviation of its values. Intense HABs were often preceded by excessive SST (up to Δσ ~1.99) and PAR (up to Δσ ~2.25) values, as well as low near-surface wind speed (up to Δσ ~−1.83). These environmental parameters considerably contribute to HAB generation and intensification. An approach and empirical function were proposed that allow us to assess the risk of HAB phenomena and reveal their precursors. Using the proposed approach and empirical function, the precursors of ten HABs were identified, nine of which were confirmed by in situ data. The results can be used as a tool for forecasting and studying the conditions for the occurrence of HABs, representing one of the promising directions for monitoring these dangerous phenomena.

Cechy charakterystyczne i parametryzacje dochodzącego promieniowania fotosyntetycznie czynnego w środkowym basenie Biebrzy = Characteristics and parametrisations of the photosynthetically active radiation incoming in the Middle Biebrza Basin

The availability of light is one of the most important factors that determine the photosynthesis process. Wave bands of solar radiation from 400 to 700 nm are called photosynthetically active radiation (PAR) because of their ability to stimulate the process of photosynthesis. The limited data availability and the regional and local PAR dependence cause the need for independent research, especially in areas of high natural value. The main goal of the work is to characterize the incoming photosynthetically active radiation in the Middle Biebrza Basin on the basis of a 9-year measurement series (2013-2021) from the Kopytkowo site (53°35'30.8”N, 22°53'32.4"E). The analysis was carried out for both instantaneous values and daily totals. In addition to the basic statistical characteristics, attention was paid to radiation on clear days and to the relationship between the PAR values on the Earth's surface and at the top of the atmosphere. Due to the limited availability of empirical data, simple parameterizations of PAR radiation were proposed for use in environmental studies. The research was carried out in the north-eastern part of Poland on the outskirts of Biebrza National Park in the Middle Biebrza Basin (Fig. 1). The area can be characterised as natural, almost unchanged, and uninhabited wetlands overgrown by swamp vegetation. The measurement site is located around 350 m north of the small village Kopytkowo with only a handful of permanent residents. The PQS1 PAR Quantum Sensor by Kipp & Zonen mounted at height 2.7 m a.g.l. was used to collect data (Fig. 2). The sensor is part of the eddy-covariance system that measures the exchange of greenhouse gases between the ecosystem and the atmosphere. Data were sampled every 10 seconds and then stored in datalogger (CR500) as 5-minute averages. The results are shown as photosynthetic photon flux density (PPFD) with micromole per square metre per second (µmol∙m⁻²∙s⁻¹) as unit and were collected in Central European Time (CET).

A novel simulation model to predict photosynthetic active radiation interception in micro-irrigated citrus production orchards based on tree spacing, canopy geometry, and row orientation

Diurnal and seasonal patterns of photosynthetically active radiation (PAR) intercepted by tree canopies in production orchards have an important role for eco-physiological processes that determine tree water use and productivity. Under well-watered conditions, PAR intercepted by trees is a reliable predictor of crop consumptive water use, which is regulated by tree spacing, tree row orientation, and by the tree canopy dimensions and geometry. Despite its advantages, only rare attempts have been made by the scientific and fruit production communities to develop canopy PAR interception simulators that rely on analytical principles to inform irrigation planning and management decisions. In this article, a novel model is presented that simulates PAR interception by citrus trees based on the canopy geometry and its shading patterns. The article also illustrates preliminary field testing and validation of the model with data collected in commercial citrus production orchards located in the San Joaquin Valley of California. The testing and validation could enable citrus growers and orchard managers to predict the net radiation for mature, micro-irrigated Navel orange and Page mandarin orchards grown with north–south and east–west tree row orientations and different tree densities. Results from the simulations and field validation showed that the canopy PAR light interception contributed 58.8 (± 0.02) and 71.1 (± 1.60) percent to the overall net radiation for the Navel orange orchards during the periods around summer solstice and autumnal equinox, respectively, whereas for the Page mandarin orchards, PAR light interception contributed 63.0 (±5.60) and 85.7 (±18.87) percent to the overall net radiation during the same time periods. Good correlations were found between daily values of PAR and net radiation for these citrus production orchards grown with the two alternative row orientations, which suggest that the proposed model could be used to inform irrigation planning and management decisions for different site-specific citrus orchard features and growing conditions.

Do Greenhouse Cover Materials Affect Cannabis Performance?


 A greenhouse pot experiment was conducted in the Agricultural University of Athens in order to evaluate the effect of several greenhouse cover materials on the performance and yield of hemp. The experiment was set up in a completely randomized design (CRD) with five treatments/greenhouses (G1, G2, G3, G4/Control, and G5). Measurements included plant height, PAR (Photosynthetic Active Radiation), chlorophyll content, solar irradiance, soil and leaf temperature, and yield components (the number of buds, their weight, length, and compact index, CBD content, and CBD yield per plant). The results of the present study suggest that the different polyethylene cover films alter the environment within the greenhouse and thus, affect the agronomic characteristics and yield traits of hemp. G1 reported the best results as it increased soil temperature and PAR values by 11-16% and 50-110% respectively, compared to G4. Concurrently, the majority of the bud characteristics were significantly improved in G1. Even though further research should be conducted in order to define the most suitable films for greenhouse hemp production, our results indicate that the optical properties of the greenhouse cover materials affect its yield and should always be considered.

Wastewater treatment potential, light penetration profile and biomass settling performance of a photo‐sequencing batch reactor

AbstractBACKGROUNDThe performance of microalgal and bacterial systems devoted to wastewater treatment might be limited by the poor settling of microalgal biomass and the inhibition of nitrifying bacteria under high irradiance conditions. This work implemented a photo‐sequencing batch bioreactor (PSBR) treating medium‐ and low‐strength wastewaters. The impact of a short settling time on the formation of microalgal–bacterial aggregates (MABAs) was evaluated. Moreover, online photosynthetically active radiation (PAR) measurements at the bottom of the PSBR were used to identify potential nitrifying activity inhibition.RESULTSA chemical oxygen demand removal efficiency of up to 88% was obtained for the medium‐ and low‐strength wastewaters. Photoinhibition of the nitrifying activity was observed at PAR values from 73 to 480 μmol m−2 s−1, and it was confirmed under non‐limiting dissolved oxygen conditions. The PSBR operating conditions, including a short settling time (30 min) and treatment of medium‐strength wastewater, favored the rapid formation of MABAs in only 19 days, with a biomass settling velocity (vs) of 0.74 m h−1. The microalgal genera Acutudesmus, Desmodesmus, and Chlorella were predominant in the MABAs. Experimental estimation of the light extinction coefficient (λ = 0.056 m2 g−1 total suspended solids) allowed the simulation of light penetration profiles at different reactor liquid depths and biomass concentrations.CONCLUSIONA short settling time favors the rapid formation of MABAs in PSBR‐type reactors treating medium‐strength wastewater. Online monitoring and simulation of light penetration is a valuable tool to determine photoinhibition of the nitrifying activity in microalgal and bacterial systems. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Biexponential decrease of PAR in coastal waters (Northern Adriatic)

The attenuation coefficients of photosynthetically active radiation (PAR) were extracted from the vertical profiles of PAR in coastal waters (the Gulf of Trieste, Northern Adriatic). The vertical profiles were collected roughly twice per month from July 2011 to December 2015, and the PAR values just above the sea surface were compared with the PAR data measured on a buoy.This research supports the nonlinear fit with the biexponential expression for the dependence of PAR with depth, yielding a much better match with the data than the fit with a mono-exponential expression. However, another reasoning for biexponential attenuation is because it functions as a solution for a homogeneous differential equation of a second order. The method for estimating the water type is offered with an analysis of the attenuation coefficients of PAR. It was found that for a particular location (the Gulf of Trieste), the attenuation coefficient in a mono-exponential decrease of PAR is 0.19-0.21 m-1, while for a biexponential decrease of PAR, the coefficient of the long-range attenuation is 0.12-0.14 m-1 and that of short-range attenuation is 0.8-0.9 m-1. This leads to the conclusion that most water columns match coastal water type 1, while the surface layer is represented by coastal water types 7 or 9. From the estimate of the water types, the coefficients of downward irradiation were inferred as 0.19 m-1∓0.01 m-1 (long-range attenua-tion) and 3.0 m-1∓0.7 m-1 (short-range attenuation). These coefficients can determine the heat source inside the water column.

Ecophysiological plasticity of Theobroma cacao L. clones in response to the structure and microclimate of agroforestry systems in Mexico

Background: Cocoa is a species commonly cultivated under agroforestry systems (AFs), when microclimate conditions are adequate, it achieves high growth rates and seed yield. Questions and Hypotheses: How do four cocoa varieties respond to open (OC) and closed (CC) shade tree canopy conditions within AFs? We hypothesized that cocoa functional traits values correlate with microclimate conditions in the CC. Studied species: Theobroma cacao L. (Malvaceae). Study site and dates: Papantla, Nautla, Veracruz; San Pedro, Oaxaca. Rainy season, 2018. Methods: Three AFs were selected; either one with OC and CC zones, photosynthetically active radiation (PAR), vapor pressure deficit (VPD), air temperature (Ta) and relative humidity (RH) were registered. Cocoa tree and leaves functional traits were evaluated in four regional cocoa varieties, in ten individuals per variety, canopy condition and AFs. Results: Higher values of PAR, VPD and Ta, and lower RH were recorded under OC than in CC. Cocoa tree height, stem diameter, fruit production, SLA (Specific Leaf Area), LWC (Leaf Water Content) and SS (Stomatal Size) were higher for Nautla. Only the cocoa clone Inifap8 displayed higher height and fruit production than the other varieties. Conclusions: Veracruz and Oaxaca states have AFs with microclimatic conditions where cocoa cultivation can potentially develop. However, it is essential to incorporate our understanding of the adaptive responses of cocoa to particular shade trees canopy structure. Cocoa leaf traits, SLA, LWC and SS, may be used as indicators for enhancing management and sustainability in AFs in the face of climate change. Translate stop Translate stop

Using the diurnal variation characteristics of effective quantum yield of PSII photochemistry for drought stress detection in maize

The importance of detecting drought stress in crops to alleviate the pressure of the growing population and food demand is well recognized. Although chlorophyll fluorescence (ChlF) is closely related to photosynthesis, it is always disturbed by the intensity of irradiance during the measurement. To detect drought stress more effectively with ChlF, we studied the diurnal relationship of the effective quantum yield of photosystem II (PSII) photochemistry (ΦPSII) and photosynthetically active radiation (PAR). We measured the diurnal ΦPSII, leaf temperature (Tleaf) and PAR of maize leaves (ZhengDan958) by pulse-amplitude modulated (PAM) fluorometry under different drought stresses. We found that in the absence of drought stress, the linearity (indicated by R2) between diurnal ΦPSII and PAR was strong. When drought stress was gradually aggravated, the difference between the ΦPSII values in the morning and those in the afternoon under similar PAR values gradually became significant. Therefore, the R2 values of the linear correlation of the diurnal ΦPSII-PAR regression gradually decreased under increased drought stress. The simulation results of a photosynthesis model showed that the diurnal variation in the response of ΦPSII-PAR during drought may be the result of the fluctuation of the substrate saturated Rubisco capacity (Vcmax) , which was dominated by the dynamics of Tleaf. The results indicated that the linearity of diurnal ΦPSII-PAR regression can be used as an effective and convenient field indicator to monitor drought stress.

Wildfire Smoke Effects on Lake‐Habitat Specific Metabolism: Toward a Conceptual Understanding

AbstractThe impacts of wildfire smoke on lake habitats remains unclear. We determined the metabolic response to smoke in the epi‐pelagic and two littoral habitats in Castle Lake, California. We compared light regime, gross primary production, ecosystem respiration, and net ecosystem production in years with and without smoke. During the smoke period incident ultraviolet‐B (UV‐B) radiation and photosynthetically active radiation (PAR) decreased by 53% and 28%, respectively, while the water column extinction coefficient of UV‐B and PAR increased by 20% and 18% respectively. Epi‐pelagic productivity increased during smoke cover because of decreased solar inputs. PAR values remained sufficient to saturate productivity, suggesting observed differences were primarily the result of changes in UV‐B. Littoral‐benthic productivity did not change, possibly reflecting adaptation to high‐intensity UV‐B light in these habitats. Our results highlight the importance of understanding how prolonged wildfire smoke alters the amount of energy produced from specific habitats in lakes.

Estimating mangrove forest gross primary production by quantifying environmental stressors in the coastal area

Mangrove ecosystems play an important role in global carbon budget, however, the quantitative relationships between environmental drivers and productivity in these forests remain poorly understood. This study presented a remote sensing (RS)-based productivity model to estimate the light use efficiency (LUE) and gross primary production (GPP) of mangrove forests in China. Firstly, LUE model considered the effects of tidal inundation and therefore involved sea surface temperature (SST) and salinity as environmental scalars. Secondly, the downscaling effect of photosynthetic active radiation (PAR) on the mangrove LUE was quantified according to different PAR values. Thirdly, the maximum LUE varied with temperature and was therefore determined based on the response of daytime net ecosystem exchange and PAR at different temperatures. Lastly, GPP was estimated by combining the LUE model with the fraction of absorbed photosynthetically active radiation from Sentinel-2 images. The results showed that the LUE model developed for mangrove forests has higher overall accuracy (RMSE = 0.0051, R2 = 0.64) than the terrestrial model (RMSE = 0.0220, R2 = 0.24). The main environmental stressor for the photosynthesis of mangrove forests in China was PAR. The estimated GPP was, in general, in agreement with the in-situ measurement from the two carbon flux towers. Compared to the MODIS GPP product, the derived GPP had higher accuracy, with RMSE improving from 39.09 to 19.05 g C/m2/8 days in 2012, and from 33.76 to 19.51 g C/m2/8 days in 2015. The spatiotemporal distributions of the mangrove GPP revealed that GPP was most strongly controlled by environmental conditions, especially temperature and PAR, as well as the distribution of mangroves. These results demonstrate the potential of the RS-based productivity model for scaling up GPP in mangrove forests, a key to explore the carbon cycle of mangrove ecosystems at national and global scales.

The effects of temperature and light on ecosystem metabolism in a Japanese stream

Ecosystem metabolism is a fundamental process that governs biogeochemical C cycling through the fixation and mineralization of C by all the organisms in a system; however, the functional responses of ecosystem metabolism to light and temperature variability remain unknown in streams and rivers. In this study, we assessed the effects of temperature and light on ecosystem metabolism, namely gross primary production (GPP) and ecosystem respiration (ER), in a Japanese stream by monitoring the seasonal diel changes in dissolved oxygen. We found that the temperature dependence of metabolism, which is expressed as activation energy, was higher for ER (0.48 eV) than for GPP (0.39 eV), supporting the metabolic theory of ecology. Both daily GPP and ER increased with the daily integrated photosynthetically active radiation (PAR), peaking at moderate PAR values and decreasing at higher irradiance levels. This unimodal relationship between daily GPP and PAR was due to the rapid increase of instantaneous PAR during the early morning, suppressing the maximum rate of area-specific productivity, which was a main determinant of daily GPP. Moreover, daily GPP and ER were closely associated in this study stream, resulting in a unimodal pattern of daily ER with daily integrated PAR. Our results suggest that both temperature and light regulate stream ecosystem metabolism but that the sunlight regime (i.e., the rapid increase of solar irradiance in the early morning) rather than light intensity per se may be a critical factor for both GPP and ER in the study stream.

PARADe: A low-cost open-source device for photosynthetically active radiation (PAR) measurements

In agriculture, proximal in-field information is crucial for a precise management of crop growth. A low-cost, miniaturized and innovative device, named PARADe (PAR Acquisition Device), is designed for in-field photosynthetically active radiation (PAR) acquisition. It combines an affordable PAR line quantum sensor (PAR/LE, SOLEMS) and an open source development platform (microcontroller) based on Arduino Integrated Development Environment. The quality of the measurement of the PARADe acquisition chain has been validated. The calibration is done by comparison (R2=0.99) with a robust acquisition chain composed of a certified PAR sensor (PQS1, Kipp and Zonen) and a data-logger (CR1000 Campbell Scientific). The accuracy of PARADe measurements is evaluated through three indicators, relative error, RMSE and normalized RMSE. They demonstrate that the PARADe system has certain operating limitations especially for low solar angles (sunset and sunrise) due to the choice of a line quantum sensor. This does not affect the accuracy and reliability of the results, but indicates that the PARADe device is specifically adapted to collect daily cumulative PAR values.

Relationship between photosynthetically active radiation and global radiation in Petrolina and Brasília, Brazil

ABSTRACT Photosynthetically active radiation (PAR) comprises the spectral range of global solar radiation (Rs) that is highly related to vegetation productivity. The study aimed to evaluate the relationship between PAR and Rs in Petrolina, PE, and Brasília, DF, Brazil, with data measured in 2011 and 2013 at two stations of the Sistema Nacional de Organização de Dados Ambientais located in Petrolina, PE and Brasília, DF, Brazil, and the obtained models were evaluated using the measurements of 2014. It was verified that the PAR, in instantaneous values (μmol m-2 s-1), can be estimated at 2.31 times the Rs (W m-2) measured in Petrolina, while for daily values of PAR (MJ m-2) is equal to 50% of Rs (MJ m-2). In Brasília, PAR (μmol m-2 s-1) is 2.05 times the Rs (W m-2) and, in daily values, equal to 44% of Rs (MJ m-2). The variability of the PAR/Rs ratio followed the local variations of clearness index (Kt) and Rs. The models presented an adequate performance based on statistical indices mean absolute error, mean relative error, and root mean square error and can be used to estimate PAR.

Retrieving high-resolution surface photosynthetically active radiation from the MODIS and GOES-16 ABI data

Incident photosynthetically active radiation (PAR) is a key parameter in plant physiological, biological and physical process-based terrestrial ecosystem models. Deriving highly accurate and spatially continuous PAR from remote sensing data can fill in the gaps of insufficient ground-based measurements. In this study, we provide an efficient approach for estimating PAR by employing look-up table (LUT) method using observations from both MODIS and GOES-16. The GOES-16 is the first satellite of the new-generation US Geostationary Operational Environmental Satellite R-series (GOES-R), which can capture dynamic changes in the atmosphere every 5 min. First, the diurnal variation of surface bidirectional reflectance is characterized assuming that the surface characteristics and solar zenith angles in tropical and middle latitudes at a given time of day do not change dramatically within a month. Next, the aerosol optical depth (AOD) and cloud optical depth (COD) are retrieved from the GOES-16 visible observations under both clear-sky and cloudy conditions. Finally, PAR is estimated via the retrieved AOD and COD using the LUT method and a MODIS-based surface albedo product. The estimated PAR was compared against ground-based measurements collected from seven SURFace RADiation budget network (SURFRAD) sites and 23 National Ecological Observatory Network (NEON) sites at instantaneous, hourly and daily scales. The instantaneous PAR validation results achieved R2 values of 0.97 and 0.82, and root mean square errors (RMSEs) of 18.1 and 51.1 W m‐2, for clear and cloudy skies, respectively. The RMSEs of the hourly averaged PAR were reduced to 16.8 W m−2 and 40.4 W m−2, respectively, for clear-sky and cloudy conditions. The daily mean PAR evaluation for all sky conditions shows an overall mean bias error (MBE) of 0.97 W m−2 and an RMSE of 10.5 W m−2. Compared with other global PAR datasets, the estimated PAR values in this study have lower RMSEs and higher spatial-temporal resolution. Uncertainties in the retrieved PAR caused by topography and solar-cloud-geometry effects (SCGE) can be reduced by spatial and temporal averaging. Based on an evaluation of retrievals at different spatial-temporal scales, we recommend that a 20 × 20 km2 domain-averaged PAR be utilized for instantaneous PAR validation, whereas hourly and daily averaged PAR values are nearly independent of spatial scale.

Intercepted Photosynthetically Active Radiation (PAR) and Spatial and Temporal Distribution of Transmitted PAR under High-Density and Super High-Density Olive Orchards

We quantified the photosynthetically active radiation (PAR) interception in a high-density (HD) and a super high-density (SHD) or hedgerow olive system, by measuring the PAR transmitted under the canopy along transects at increasing distance from the tree rows. Transmitted PAR was measured every minute, then cumulated over the day and the season. The frequencies of the different PAR levels occurring during the day were calculated. SHD intercepted significantly but slightly less overall PAR than HD (0.57 ± 0.002 vs. 0.62 ± 0.03 of the PAR incident above the canopy) but had a much greater spatial variability of transmitted PAR (0.21 under the tree row, up to 0.59 in the alley center), compared to HD (range: 0.34–0.43). This corresponded to greater variability in the frequencies of daily PAR values, with the more shaded positions receiving greater frequencies of low PAR values. The much lower PAR level under the tree row in SHD, compared to any position in HD, implies greater self-shading in lower-canopy layers, despite similar overall interception. Therefore, knowing overall PAR interception does not allow an understanding of differences in PAR distribution on the ground and within the canopy and their possible effects on canopy radiation use efficiency (RUE) and performance, between different architectural systems.

Incident photosyntehticaly active radiation under and outside the canopy of Acacia nilotica (Linn.) for agroforestry system

The important factor to be considered in biomass production is the maximum light use efficiency. The capture of radiation and its use in dry matter production depends on the fraction of the incident photosynthetically active radiation (PAR). An experiment was conducted in the campus of Dr. Panjabrao Deshmukh Krishi Vidyapeeth Akola, Maharashtra during 2018-2019 with the objective to study microclimatic effect under Babul (Acacia nilotica L.) for checking the suitability of Babul to match the under story agricultural crops and pasture grasses on the basis of microclimatic parameters recorded under and outside the canopy of Babul. Collected data were statistically analyzed with descriptive statistics by calculating mean and standard deviation. Observations on microclimatic parameters Photosynthetically active radiation were recorded from October to December (Rabbi Season). Observations were recorded under and outside the canopy of Babul by selecting ten trees from the 15x15 m plot of Babul plantation site and data were recorded during (9 am, 2pm, and 4pm) in a day by weekly intervals for three months. The results revealed that the microclimatic parameter such as photosynthetically active radiation (PAR) showed lower values under the canopy and higher value outside the canopy, and from West and South direction highest PAR was recorded. In comparison, average PAR values under the canopy from all the three months were lower for the outside canopy PAR value. On the basis of this farmer can chose the suitable understory agricultural crops and pasture grasses.

Consistent retrieval of multiple parameters from GOES-R top of atmosphere reflectance data

ABSTRACT Current remote sensing products are mainly generated from polar-orbiting satellite data using parameter-specific algorithms. These products lack physical consistency and cannot accurately characterize intra-day variations of parameters, such as the fraction of absorbed photosynthetically active radiation (FAPAR) and surface albedo. In this study, a multi-parameter consistent retrieval method is proposed to simultaneously retrieve aerosol optical depth (AOD), leaf area index (LAI), photosynthetically active radiation (PAR), FAPAR, surface albedo, and incident shortwave radiation (ISR) from top of atmosphere (TOA) reflectance data acquired by the Advanced Baseline Imager (ABI) aboard the Geostationary Operational Environmental Satellite-R series (GOES-R). The retrieved parameter values were evaluated through comparisons with corresponding Moderate Resolution Imaging Spectroradiometer (MODIS), the second version of the Geoland2 (GEOV2), and GOES-R products and ground measurements over five surface radiation budget network (SURFRAD) sites with different vegetation types. The results demonstrate that the retrieved AOD, PAR, ISR, and surface albedo values have consistent intra-day variations with the ground measurements, and the retrieved parameter values achieve good performance against the ground measurements for all the five SURFRAD sites. The root mean square errors of the retrieved AOD, shortwave albedo, ISR, and PAR values against the ground measurements are 0.071, 0.032, 50.943 W m–2, and 27.975 W m–2, respectively.