Estimation method of daily global radiation under different sunshine conditions: A case study of Jiangsu Province
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摘要: 太阳辐射是影响农田生态系统碳交换和能量收支等的关键因子。为了准确估算不同日照情况下的太阳日辐射量, 更好地开展农田生态系统的相关研究, 本文以江苏省为例, 利用淮安、吕泗和南京3个辐射观测站2005—2020年逐日气象资料和辐射资料, 以逐日日照时数是否为0, 将研究样本划分为无日照和有日照两类, 梳理了可观测得到的24个气象因子、3个地理因子, 通过相关分析确定了不同日照情况下太阳日辐射的高度相关因子; 选取3个站2005—2016年奇数年份的逐日资料样本作为建模集, 采用基于最小二乘法的逐步回归方式, 分别以太阳日辐射(GR)和日大气透明系数(太阳日辐射与天空辐射的比值, GR/SR)作为因变量建立了不同日照情况下的太阳日辐射估算模型; 选取3个站2005—2016年偶数年份的逐日资料样本为组间验证集、2017—2020年的逐日资料样本为组外验证集。通过比较模型的拟合效果及其对建模集、组间验证集和组外验证集太阳日辐射的估算效果, 最终确定太阳日辐射估算的最佳模型。结果表明: 1)无论是在无日照情况还是有日照情况下, 太阳日辐射都与各气象因子普遍呈现极显著相关(P<0.01)。其中在有日照情况下, 太阳日辐射与日照因子呈最强的相关性, 而在无日照情况下, 太阳日辐射与日最高地表温度表现出最强的相关性, 两者之间的相关系数高于其他气温类因子。2)无日照情况下应选择以太阳日辐射为因变量、以日最高地表温度和日露点温度为自变量的估算模型, 模型的决定系数R2为0.650, 对太阳日辐射的估算准确度接近75%; 在有日照情况下选择以日大气透明系数为因变量、以日日照百分率和日日照时数为自变量集的估算模型, 模型的决定系数R2可达0.769, 对太阳日辐射的估算准确度平均为87.60%。基于该分段估算模型, 江苏地区不同日照情况下的太阳日辐射估算准确度平均可达84.71%, 异常点占比为2.04%。引入准确的太阳辐射量将利于更好地开展作物生长和产量模拟、土壤水分蒸散估算等研究, 最终为农田生态系统的相关研究提供基础。Abstract: Global radiation is a key factor affecting carbon exchange and the surface energy budget of agroecosystems. To accurately estimate the daily global radiation (GR) under different sunshine conditions and to improve the research carried out on agroecosystems, this study used daily meteorological and radiation data collected between 2005 and 2020 at three radiation observation stations in Jiangsu Province, namely Huai’an, Lüsi, and Nanjing, to divide the research samples into two categories, namely with and without sunshine, according to whether the number of hours of sunshine per day was zero. In total, 24 observable meteorological factors and 3 geographical factors were identified, with the main factors influencing GR under different sunshine conditions being determined using correlation analysis. Daily data from the three stations collected during odd-numbered years between 2005 and 2016 were selected as the modeling dataset, and the least-squares stepwise regression method was adopted to establish the GR estimation models for conditions with and without sunshine, with GR and the daily atmospheric transparency coefficient (ratio of GR to sky radiation [SR], GR/SR) representing the dependent variables. Daily data samples from the three stations collected during even-numbered years between 2005 and 2016 were selected as the between-group verification set, while daily data samples collected from 2017 to 2020 were selected as outside-group verification sets. The optimal GR estimation model for Jiangsu Province was determined by comparing the model fits and the estimation effects of the original models with the between-group and the outside-group verification sets. The results showed that first, GR was significantly correlated with most of the meteorological factors (P<0.01) regardless of the presence of sunshine. GR under sunshine conditions had the strongest correlation with sunshine factors, while GR under without sunshine condition had the strongest correlation with the daily maximum ground temperature (TGMax). Furthermore, the correlation coefficient between GR and TGMax was higher than the correlation between GR and other temperature factors. Second, the estimation model with GR as the dependent variable and TGMax and daily dew point temperature as the independent variables was selected when the daily sunshine duration was zero; the coefficient of determination (R2) of this model was 0.650, and the estimation accuracy of GR was close to 75%. The estimation model with GR/SR as the dependent variable and daily percentage of sunshine and sunshine duration as the independent variables was selected when the daily sunshine duration was greater than zero; the R2 of this model reached 0.769 and the average estimation accuracy of GR was 87.60%. On the basis of subsection of estimation models, the average accuracy of GR under different sunshine conditions in Jiangsu reached 84.71%, and the proportion of outliers in the total sample was 2.04%. The introduction of accurate GR estimation is greatly beneficial to carry out research on crop growth and yield simulation and soil moisture estimation, and ultimately provide a basis for related research on agroecosystems.
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Key words:
- Daily global radiation /
- Sunshine hours /
- Stepwise regression /
- Sunshine condition /
- Estimation method
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图 2 无日照(A, n=1515)和有日照(B, n=5050)天气情况下太阳日辐射与环境因子的相关性
CT: 逐日平均总云量; CL: 逐日平均低云量; P: 逐日平均气压; PMax: 逐日最高气压; PMin: 逐日最低气压; e: 逐日平均水汽压; eMax: 逐日最高水汽压; eMin: 逐日最低水汽压; T: 逐日平均气温; TMax: 逐日最高气温; TMin: 逐日最低气温; TR: 逐日气温日较差; TG: 逐日平均地表温度; TGMax: 逐日最高地表温度; TGMin: 逐日最低地表温度; TDP: 逐日露点温度; S: 逐日日照时数; SR: 逐日日照百分率; RH: 逐日相对湿度; R: 逐日降水量; Evp: 逐日蒸发量; Lo: 经度; La: 纬度; H: 海拔; GR: 逐日太阳日辐射。CT: daily total cloud cover; CL: daily low cloud cover; P: daily average atmospheric pressure; PMax: daily maximum atmospheric pressure; PMin: daily minimum atmospheric pressure; e: daily average vapour pressure; eMax: daily maximum vapour pressure; eMin: daily minimum vapour pressure; T: daily average temperature; TMax: daily maximum temperature; TMin: daily minimum temperature; TR: daily diurnal temperature range; TG: daily average surface temperature; TGMax: daily maximum ground temperature; TGMin: daily minimum ground temperature; TDP: daily dew point temperature; S: daily sunshine duration; SR: daily percentage of sunshine; RH: daily relative humidity; R: daily precipitation; Evp: daily evaporation; Lo: longitude; La: latitude; H: elevation; GR: daily global radiation.
Figure 2. Correlation between daily global radiation and environmental factors under without sunshine (A, n=1515) and sunshine (B, n=5050) conditions
图 4 建模集和验证集基于模型F1和F4的太阳日辐射模拟值-实际值的散点分布图(a: 无日照建模集基于模型F1; b: 有日照建模集基于模型F4; c: 无日照组间验证集基于模型F1; d: 有日照组间验证集基于模型F4; e: 无日照组外验证集基于模型F1; f: 有日照组外验证集基于模型F4)
Figure 4. Scatter distribution diagrams of actual and simulated daily global radiation of models F1 and F4 based on establishment and validation datasets (a: model F1 based on establishment dataset under without sunshine condition; b: model F4 based on establishment dataset under sunshine condition; c: model F1 based on between-group validation dataset without sunshine condition; d: model F4 based on between-group validation dataset under sunshine condition; e: model F1 based on outside-group validation dataset without sunshine condition; f: model F4 based on outside-group validation dataset under sunshine condition)
表 1 有无日照天气情况下基于气象因子和天空辐射的太阳日辐射回归估算模型结构
Table 1. Structure of regression estimation models for daily global radiation under with and without sunshine conditions based on meteorological factors and radiation
模型
Model自变量
Independent variable因子数量
Number of factors因变量
Dependent variable无日照
Without sunshineF1 气象因子
Meteorological factors25 太阳日辐射
Daily global radiation (GR)F2 气象因子、天空辐射
Meteorological factors and sky radiation24 大气透明系数
Daily atmospheric transparency coefficient (GR/SR)有日照
Under sunshineF3 气象因子
Meteorological factors25 太阳日辐射
Daily global radiation (GR)F4 气象因子、天空辐射
Meteorological factors and sky radiation24 大气透明系数
Daily atmospheric transparency coefficient (GR/SR)表 2 有无日照天气情况下基于气象因子和天空辐射的太阳日辐射回归估算模型
Table 2. Estimation models of daily global radiation under without sunshine and sunshine conditions based on meteorological factor and radiation
模型 Model 模型表达式 Model expression R2 F P 无日照
Without sunshineF1 GR=0.427TGMax−0.322 TDP−0.643 0.650 1405.750 0.000 F2 GR/SR=−0.030CT−0.003RH−0.001R+0.001TGMax+0.673 0.382 234.219 0.000 有日照
Under sunshineF3 GR=1.437S+5.401 0.592 7324.189 0.000 F4 GR/SR=1.281SR−0.067S+0.226 0.769 8405.086 0.000 GR为太阳日辐射, GR/SR为大气透明系数, TGMax为最高地表气温, TDP为露点温度, CT为总云量, RH为相对湿度, R为降水量, S为日照时数, SR为日照百分率。GR is the daily global radiation; GR/SR is the daily atmospheric transparency coefficient (ratio of global radiation to sky radiation); TGMax is the daily maximum ground temperature; TDP is the daily dew point temperature; CT is the daily total cloud cover; RH is the daily relative humidity; R is the daily precipitation; S is the daily sunshine duration; SR is the daily relative sunshine duration. 表 3 有无日照天气情况下不同太阳日辐射回归估算模型在不同数据集估算效果
Table 3. Estimation effects of models of daily global radiation under without sunshine and sunshine conditions in different datasets
% 模型
Models建模集
Establishment dataset组间验证集
Between-group validation dataset组外验证集
Outside-group validation dataset平均
Average异常点比例
Proportion of outliers估算准确度
Estimation accuracy异常点比例
Proportion of outliers估算准确度
Estimation accuracy异常点比例
Proportion of outliers估算准确度
Estimation accuracy异常点比例
Proportion of outliers估算准确度
Estimation accuracy无日照
Without sunshineF1 7.11 75.11 6.22 74.41 3.37 73.98 5.89 74.57 F2 11.59 68.29 11.68 69.51 6.64 69.28 10.51 69.00 有日照
Under sunshineF3 0.79 77.31 0.88 77.20 1.84 76.94 1.09 77.18 F4 0.83 87.93 0.66 88.44 1.28 85.87 0.88 87.60 -
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