基于日照时数的光合有效辐射(PAR)时数估算方法

Estimation of photosynthetically active radiation( PAR) using sunshine duration

光合有效辐射(PAR)是影响光合生产潜力的重要因素,传统气候学计算PAR值的方法所需参数较多,且对天气变化敏感、精度较差。为此,基于容易获得的实际监测日照时数与理论计算日照时数比值,提出了一种估算PAR强度超过一定阈值(最低值>300μmol·m-2·s^(-1))时间长度的方法,与日照时数对应,定义为PAR时数。将PAR时数估算值与7年间超过不同光照阈值(27、36、100、200、300、360、450和900μmol·m-2·s^(-1))的PAR时数实测值进行对比,分析了监测时间长度、季节、天气情况对PAR时数估算精度的影响。结果表明:PAR值>300μmol·m-2·s^(-1)、监测时间≥4年,PAR时数估算值与实测值无显著差异;监测时间越长,PAR时数估算精度越高。虽然秋季与春季估算精度好于夏季;晴天与多云天气估算精度好于阴天,但鉴于长期、全生长季的结果更能反映真实情况,因此,本研究建议采用生长季长期监测的方法(监测时间至少为4年)利用日照时数估算>300μmol·m-2·s^(-1)以上的PAR时数。

Photosynthetically active radiation （PAR） is an important factor indicating the photo- synthetic productive potential. Traditional PAR estimation methods, however, need much more climatic parameters, and are sensitive to weather conditions and low in accuracy. Thus, we pro- vided a new method to estimate PAR duration, which is defined as the duration when PAR ex- ceeds a certain value, e.g., 300 μmol·^-2·s^-1 in a day of the growing season, using the ratios of observed sunshine duration （the most common index in each meteorological station） to theore- tical sunshine duration. We monitored both sunshine duration and PAR duration for 7 years. The paired values of observed and estimated PAR durations based on different thresholds （27, 36, 100, 200, 300, 360, 450 and 900 μmol·^-2·s^-1） were collected. The effects of monitoring time length, seasons and weather conditions on the accuracy of estimated PAR duration were ana- lyzed. There were no significant differences between estimated PAR durations （mean values） and the observed values （P〉0.05） when the monitoring time length was equal or greater than 4 years for PAR〉300 μmol·^-2·s^-1. The accuracy of the estimated PAR duration was higher when the monitoring time length became longer; it was lower in summer than in spring and autumn, and lower in cloudy sky than in sunny and fair weather. We recommended the use of long-term （at least 4 years） observations of sunshine duration to estimate the duration of PAR 〉300 μmol·^-2·s^-1 because the overall effects of the weather conditions in whole growing season can be reflec- ted by the long term observations.