Preliminary validation of leaf area index sensor in Huailai
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Leaf area index (LAI) is a key variable in many land surface models that involve energy and mass exchange between vegetation and the environment. In recent years, extracting vegetation structure parameters from digital photography becomes a widely used indirect method to estimate LAI for its simplicity and ease of use. A Leaf Area Index Sensor (LAIS) system was developed to continuously monitor the growth of crops in several sampling points in Huailai, China. The system applies 3G/WIFI communication technology to remotely collect crop photos in real-time. Then the crop photos are automatically processed and LAI is estimated based on the improved leaf area index of Lang and Xiang (LAILX) algorithm in LAIS. The objective of this study is to primarily verify the LAI estimated from LAIS (Lphoto) through comparing them with the destructive green LAI (Ldest). Ldest was measured across the growing season ntil maximum canopy development while plants are still green. The preliminary verification shows that Lphoto corresponds well with the Ldest (R2=0.975). In general, LAI could be accurately estimated with LAIS and its LAI shows high consistency compared with the destructive green LAI. The continuous LAI measurement obtained from LAIS could be used for the validation of remote sensing LAI products.Interception
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Interception
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The dynamic change of moso bamboo(Phyllostachys edulis) canopy parameters,including total chlorophyll content(TCC),leaf area index(LAI),canopy closure(CC) during the bamboo shooting growth phase was examined,and the relationships between these canopy parameters and photosynthetic active radiation(PAR) were analyzed.Results showed(1) increases in TCC,LAI,and CC during the bamboo shooting growth phase;(2) that the relationship between a mother bamboo's TCC and PAR in the prior leaf development stage(R = 0.570,P = 0.180) was higher than in the posterior leaf development(R = 0.140,P = 0.860);and(3) after leaf development,PAR had a positive correlation with LAI(R2 = 0.796 0,P = 0.120) and a significantly positive correlation with CC(R2 = 0.991 6,P = 0.004).This result implied that the priority for delivering photosynthetic products from the mother bamboo was to shoot before leaf development.The correlation analysis showed that the Phyllostachys edulis canopy enhanced solar energy allocation and utility.
Phyllostachys edulis
Phyllostachys
Photosynthetically active radiation
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Global products of vegetation green Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) are being operationally produced from Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) at 1-km resolution and eight-day frequency. This paper summarizes the experience of several collaborating investigators on validation of MODIS LAI products and demonstrates the close connection between product validation and algorithm refinement activities. The validation of moderate resolution LAI products includes three steps: 1) field sampling representative of LAI spatial distribution and dynamic range within each major land cover type at the validation site; 2) development of a transfer function between field LAI measurements and high resolution satellite data to generate a reference LAI map over an extended area; and 3) comparison of MODIS LAI with aggregated reference LAI map at patch (multipixel) scale in view of geo-location and pixel shift uncertainties. The MODIS LAI validation experiences, summarized here, suggest three key factors that influence the accuracy of LAI retrievals: 1) uncertainties in input land cover data, 2) uncertainties in input surface reflectances, and 3) uncertainties from the model used to build the look-up tables accompanying the algorithm. This strategy of validation efforts guiding algorithm refinements has led to progressively more accurate LAI products from the MODIS sensors aboard NASA's Terra and Aqua platforms
Moderate-resolution imaging spectroradiometer
Spectroradiometer
Land Cover
Photosynthetically active radiation
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SunScan canopy analysis system is an instrument for indirectly measuring leaf area index (LAI). The instrument can give LAI values by measuring the ratio of transmitted radiation through canopy to incident radiation, based on the canopy geometry features described by ellipsoidal leaf angle distribution parameter (ELADP). In 2005 and 2006, the LAI values of soybean plants at the Heshan Farm of Nenjiang County, Heilongjiang Province were measured with LI-3100 LAI apparatus and SunScan canopy analysis system, the ELADP value was calibrated for accurate LAI, and the precision of the LAI values measured by SunScan canopy analysis system was validated. The results showed that the ELADP value for soybean canopy was 4.0, and the LAI values measured by SunScan canopy analysis system were consistent with those measured by LI-3100. The regression correlation of the LAI values measured by the two instruments was significant. During the growth season of soybean, the measurement error of SunScan canopy analysis system had a slight change, i.e., the LAI was underestimated by 7.2% from 50 to 85 days after sowing and overestimated by 12.5% from 96 days after sowing, but close to that measured by LI-3100, with an error of 2.0%. In conclasion, SunScan canopy analysis system could be used to measure the LAI accurately if the ELADP was calibrated for different canopies.
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Abstract With the increased use of variables such as canopy cover, photosynthetically active radiation (PAR) and overstory leaf area index (LAI) in forestry research, relationships between these variables and traditional forestry variables must be defined before recommended levels of these research variables can be achieved by forestry practitioners on the ground. We measured basal area, canopy cover, Ozalid percent full light, PAR, and overstory LAI in thinned and unthinned plots within oak and pine stands with the objectives of: (1) determining the relationships between these variables in two common forest types, (2) investigating the feasibility of using basal area to estimate and achieve recommended levels of canopy cover, PAR, and LAI in the field, and (3) examining the possibility of using direct canopy cover and Ozalid light measurements for estimating PAR and LAI. Very strong relationships (r² > 0.90 and P < 0.0001) were indicated between basal area and canopy cover, PAR, and LAI. Direct canopy cover and Ozalid light measurements were also strongly related to PAR and LAI. It is likely that the even-aged structure of the stands studied contributed to these results. The strength of the relationships between the measures examined suggest that practical variables such as basal area could potentially be used by forestry practitioners to estimate and achieve recommended levels of canopy cover, PAR, and LAI in similar oak and pine stands. The possibility also exists for strong relationships between these variables in other stand types that resemble those studied in terms of overstory structure. North. J. Appl. For. 16(1):25-32.
Basal area
Photosynthetically active radiation
Plant cover
Tree canopy
Understory
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Leaf area index (LAI), as an important characterization parameter, reflects the canopy structural characteristics of crops. It is commonly used to estimate foliage cover, as well as forecasting crop growth and yield [1,2,3]. Because LAI is functionally linked to the canopy spectral reflectance, its retrieval from remote sensing data has prompted many investigations and studies in recent years. The common and widely used approach has been to develop relationships between ground-measured LAI and vegetation indices [1,4,5]. These vegetation indices performed well at the early stage of crop growth, but the estimation accuracy are greatly decreased in the late growth stages, especially after heading stage. A major problem in the use of these indices arises from the fact that canopy reflectance, it is strongly dependent on both structural and biochemical properties of the canopy [6,7,8]. In the late period of crop growth, panicles changed the canopy structure of crops and affected the crop canopy spectral reflectance [9,10]. This study compared the accuracy of monitoring LAI by using the spectral reflectance that measured the entire canopy and those canopies with panicles removed, and proposed a convenient method to removal of the effect of panicles on canopy reflectance and to enhance the prediction accuracy of LAI after heading stage of rice.
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Photochemical Reflectance Index
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