Average Reflectance Values Research Articles

Discrimination of mangrove species and mudflat classes using in situ hyperspectral data: a case study of Indian Sundarbans

This study attempts to assess whether canopy spectra of mangrove species and mudflat spectra recorded under field conditions contain adequate spectral information for discerning mangroves at species rank and mudflats at the class level. This article highlights the hyperspectral characteristics of canopies of 17 tropical mangrove species, belonging to nine families, creek water and four mudflat classes found in the tidal forests of Indian Sundarbans. Hyperspectral observations were recorded using a field spectroradiometer, and pre-processed and averaged reflectance values of samples were subjected to various statistically tests such as k-means cluster analysis, one-way analysis of variance (ANOVA), stepwise linear discrimination and factor analysis. k-means cluster analysis showed highest Euclidean distance between Rhizophoraceae and Myrsinaceae/Plumbaginaceae. ANOVA results indicated that all the canopy spectra were statistically different at all the spectral locations except one with majority of the bands exhibiting 99% confidence level, and for the mudflat classes and creek water, all bands showed p < 0.01. Discriminant analysis was performed in different combinations/cases to identify the bands for maximum separability. Optimal Wilks' Lambda (L) were achieved with two, six, four, eight, one, four, two and three for differentiating canopies of the species of Avicennia, Sonneratia, Xylocarpus, Bruguiera, Ceriops, Bruguiera and Rhizophora, all species of Rhizophoraceae, two species of Arecaceae, respectively. For mudflat classes and creek water, the best possible Wilks' Lambda were attained with four, five and two for discriminating upper, intermediate and mud lower, mud lower and water, mud upper with and without roots, correspondingly. Factor analysis was the tool used to identify the wavelengths that were uncorrelated and contained maximum information in the combination of selected wavelengths. The most significant bands for canopy discrimination were 960, 970, 1000, 1070, 1120, 1160, 2070, 2080, 2150, 2200, 2240 and 2340 nm; for discrimination amongst mudflat classes and creek water, the bands were 540, 550, 730, 740, 770, 780, 880, 1190, 1290, 2010 and 2150 nm. Overall, hyperspectral data showed potential for discriminating between mangrove canopies of different species and for discerning mudflat classes. The outcomes of the study also indicated the efficacy of the applied statistical tools for discrimination.

Optimization of ZnO:Al based back reflectors for applications in thin film flexible solar cells

Back reflectors based on Aluminum and Molybdenum as the reflecting materials and ZnO:Al as the transparent conductive oxide, were deposited at low temperature on polyethylene naphthalate by magnetron sputtering. The optimization of the layer thickness of the constituent materials and the final texture of the structure was performed in order to achieve structures with appropriate properties to be applied to amorphous silicon solar cells. In this sense, average total reflectance values of 71% in the wavelength range of 400–800 nm were obtained for the layer stack of 80 nm-thick ZnO:Al layer on 235 nm-thick Aluminum deposited directly on the flexible substrate. However, this structure showed a poor adherence onto the substrate. This issue was improved using a thin Molybdenum layer between the metal and the substrate, maintaining similar optical properties. On the other hand, textured back reflectors were obtained etching the transparent conductive oxide with NH4Cl aqueous solution. After the etching process, the highest enhancement was achieved for the sample that used an Mo/Al bilayer as reflective metal. In this case, a roughness of around 29 nm and a haze factor of 25% at 600 nm were achieved.

Reflectance measurements of zooclasts and solid bitumen in Lower Paleozoic shales, southern Scandinavia: Correlation to vitrinite reflectance

Reflectance measurements have been carried out on zooclasts (graptolites, chitinozoans, and vase-shaped microfossils) and other organic particles (vitrinite-like particles, porous/granular vitrinite-like particles, and solid bitumen) in Middle Cambrian to Upper Silurian shales from central and southern Sweden and the Danish island of Bornholm (Baltic Sea). The most abundant organic components in all the shales are fragments of graptolites and vitrinite-like particles. The reflectance distribution of these two types of components is largely identical, and it is suggested that the vitrinite-like particles are fragments of graptolites without any recognizable morphology. Reflectance measurements of graptolites and vitrinite-like particles yield well-defined reflectance populations. In samples with average Rgraptolite and average Rvitrinite-like of >0.75%Ro, the reflectance distributions are bimodal because of increasing bireflectance, and the average reflectance value of the well-defined lower reflecting population is arbitrarily used as maturity indicator. Our results suggest that with increasing thermal maturity the reflectance of graptolites increases faster than the predicted vitrinite reflectance. The relationship between graptolite reflectance and equivalent vitrinite reflectance can be expressed by the equation: VReqv=0.73R(graptolite+vitrinite-like)low+0.16. The ‘gas generation window’, which normally is considered to begin at a vitrinite reflectance of 1.3%Ro in post-Lower Paleozoic rocks containing vitrinite, starts, accordingly, at 1.56%Ro graptolite reflectance. Porous/granular vitrinite-like particles occur in minor amounts and they may represent graptolite fragments with a non-smooth surface. They generally yield slightly higher reflectance than non-granular vitrinite-like particles and graptolite fragments. The Middle Cambrian to Furongian (upper Cambrian) shales may contain sparse fragments of vase-shaped microfossils (VSM) that seem to follow the maturation trend of chitinozoans. In the present sample set, the reflectance of chitinozoans and VSM is comparable to that of graptolites at the same level of maturity. Reflectance measurements of solid bitumen are a poor maturity indicator, probably because bitumen can have various origins and morphologies and it may not be indigenous to the host rock.

Huanglongbing (Citrus Greening) Detection Using Visible, Near Infrared and Thermal Imaging Techniques

This study demonstrates the applicability of visible-near infrared and thermal imaging for detection of Huanglongbing (HLB) disease in citrus trees. Visible-near infrared (440–900 nm) and thermal infrared spectral reflectance data were collected from individual healthy and HLB-infected trees. Data analysis revealed that the average reflectance values of the healthy trees in the visible region were lower than those in the near infrared region, while the opposite was the case for HLB-infected trees. Moreover, 560 nm, 710 nm, and thermal band showed maximum class separability between healthy and HLB-infected groups among the evaluated visible-infrared bands. Similarly, analysis of several vegetation indices indicated that the normalized difference vegetation index (NDVI), Vogelmann red-edge index (VOG) and modified red-edge simple ratio (mSR) demonstrated good class separability between the two groups. Classification studies using average spectral reflectance values from the visible, near infrared, and thermal bands (13 spectral features) as input features indicated that an average overall classification accuracy of about 87%, with 89% specificity and 85% sensitivity could be achieved with classification models such as support vector machine for trees with symptomatic leaves.

Multi-functional antireflective surface-relief structures based on nanoscale porous germanium with graded refractive index profiles

We fabricated the multi-stacked graded refractive index (GRIN) porous amorphous germanium (a-Ge) films with linear, quintic, and Gaussian index profiles for their refractive indices at a wavelength of 1.33 μm by e-beam evaporation with a glancing angle deposition technique. The porous a-Ge films with inclined nanocolumnar structures were deposited on Ge substrates at incident vapor flux angles of 40, 55, and 75°. The surface wetting behaviour of the porous a-Ge films was explored, exhibiting the hydrophilic surfaces with water contact angles below 78°. Their optical reflectance properties were investigated, together with the theoretical analysis using the rigorous coupled-wave analysis simulation. For the GRIN a-Ge films with a quintic index profile, a low reflectance band of <2% was shifted towards the longer wavelength with increasing the total thickness (ttotal) of GRIN a-Ge layers. For the GRIN a-Ge films with optimized ttotal values of 350, 333, and 225 nm for linear, quintic, and Gaussian index profiles, respectively, the low reflectance spectra of <10% were obtained at wavelengths of 1.1-1.7 μm, which yielded the lowest average reflectance value (Ravg) of ∼2.2% for Gaussian index profile (compared to the Ravg ∼ 3.7 and 4% for linear and quintic ones, respectively). The angle-dependent reflectance characteristics were also studied at incident angles of 15-85° for s- and p-polarized lights at a wavelength of 1.33 μm. The calculated results showed similar trends to the experimental data.

HIGH‐RESOLUTION STRATIGRAPHY, PALYNOFACIES AND SOURCE ROCK POTENTIAL OF THE ÁGUA DE MADEIROS FORMATION (LOWER JURASSIC), LUSITANIAN BASIN, PORTUGAL

In the Lusitanian Basin (central‐western Portugal), the Lower Jurassic carbonate‐dominated succession is thought to have significant source rock potential. One of the most important units is the Água de Madeiros Formation (Upper Sinemurian – lowermost Pliensbachian) which is composed of alternating organic‐rich marls and limestones including black shale horizons. This paper is based on a study of this formation at its type locality at S. Pedro de Moel in western Portugal. Data includes Total Organic Carbon (TOC) measurements, palynofacies analyses and results of Rock‐Eval pyrolysis presented within a high‐resolution lithostratigraphic framework.TOC contents were measured in some 200 samples from the Água de Madeiros Formation covering a stratigraphic interval of 58 m, and vary widely up to a maximum of about 22 wt %. Kerogen assemblages are dominated by marine amorphous organic matter with varying contributions by phytoclasts and palynomorphs. A majority of the 85 samples analyzed by Rock‐Eval pyrolysis have S2 values above 10 mg HC/g rock, reaching a maximum of 78 mg HC/g rock. These high S2 values are correlative with maximum values of the Hydrogen Index which averages 355 mg HC/g TOC (maximum of 637 mg HC/g TOC). However in spite of these indicators of source‐rock potential, the Água de Madeiros Formation in the study area is thermally immature or very early mature, as indicated by Tmax values below 437 °C and average vitrinite reflectance values of 0.43 % Ro.

Sea ice properties in the Bohai Sea measured by MODIS-Aqua: 2. Study of sea ice seasonal and interannual variability

During the 2009–2010 winter, the Bohai Sea experienced its most severe sea ice event in four decades, which caused significant economic losses, affected marine transportation and fishery, and impacted the entire marine ecosystem in the region. Measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite from 2002 to 2010 and surface atmosphere temperature (SAT) data from the National Centers for Environmental Prediction (NCEP) are used to study and quantify the extreme sea ice event in the 2009–2010 winter and the interannual variability of the regional sea ice properties, as well as the relationship between sea ice and the climate variability in the Bohai Sea. The mean sea ice reflectance from MODIS-Aqua visible and near-infrared wavelengths are 9.33%, 13.26%, and 12.60% in the months of December 2009, January 2010, and February 2010, respectively, compared with the monthly average sea ice reflectance values (from 2002 to 2010) of 9.35%, 11.21%, and 11.41% in the same three winter months. The sea ice monthly average coverages are ~5427, ~27,414, and ~21,156km2 in these three winter months. These values are significantly higher than the averages of monthly sea ice coverage of ~2735, ~11,119, and ~10,287km2 in the Bohai Sea in December, January, and February between 2002 and 2010. Most of the sea ice coverage was located in the northern Bohai Sea. Both the intra-seasonal and interannual sea ice variability in the Bohai Sea is found to be related closely to SAT. The mechanism of anomalous SAT and intense sea ice severity are also discussed and attributed to large-scale climate changes due to the variability of the Arctic Oscillation (AO) and Siberian High (SH).

Use of Variogram Parameters in Analysis of Hyperspectral Imaging Data Acquired from Dual-Stressed Crop Leaves

A detailed introduction to variogram analysis of reflectance data is provided, and variogram parameters (nugget, sill, and range values) were examined as possible indicators of abiotic (irrigation regime) and biotic (spider mite infestation) stressors. Reflectance data was acquired from 2 maize hybrids (Zea mays L.) at multiple time points in 2 data sets (229 hyperspectral images), and data from 160 individual spectral bands in the spectrum from 405 to 907 nm were analyzed. Based on 480 analyses of variance (160 spectral bands × 3 variogram parameters), it was seen that most of the combinations of spectral bands and variogram parameters were unsuitable as stress indicators mainly because of significant difference between the 2 data sets. However, several combinations of spectral bands and variogram parameters (especially nugget values) could be considered unique indicators of either abiotic or biotic stress. Furthermore, nugget values at 683 and 775 nm responded significantly to abiotic stress, and nugget values at 731 nm and range values at 715 nm responded significantly to biotic stress. Based on qualitative characterization of actual hyperspectral images, it was seen that even subtle changes in spatial patterns of reflectance values can elicit several-fold changes in variogram parameters despite non-significant changes in average and median reflectance values and in width of 95% confidence limits. Such scattered stress expression is in accordance with documented within-leaf variation in both mineral content and chlorophyll concentration and therefore supports the need for reflectance-based stress detection at a high spatial resolution (many hyperspectral reflectance profiles acquired from a single leaf) and may be used to explain or characterize within-leaf foraging patterns of herbivorous arthropods.

Hyperspectral leaf signature as an added dimension for species discrimination: case study of four tropical mangroves

Hyperspectral leaf reflectance of a plant provides unique information that is characteristic of that plant. The present investigation is a preliminary attempt to assess whether spectra of leaves of mangrove species recorded under field conditions contain adequate spectral information for discerning mangroves at species rank. The paper highlights the hyperspectral characteristics of leaf surfaces of four prominent tropical mangrove species, viz., Avicennia alba, Avicennia marina, Rhizophora mucronata and Sonneratia caseolaris, found in the tidal forests of India. Hyperspectral observations were recorded using a field spectroradiometer, and pre-processed and averaged reflectance values of samples for three types of arrangements, viz., (1) randomly arranged leaves, (2) dorsal leaf surfaces and (3) ventral leaf surfaces of the species were statistically tested using one-way ANOVA to see whether the values significantly differed at every spectral location. All the four species were statistically different at all the spectral locations with majority of the bands exhibiting 99% confidence level. Finally, discriminant analysis was performed to identify the bands for maximum separability for the three types of arrangement of the leaves of the species taken separately and in different combinations. The optimal Wilks’ Lambda (L) were achieved with: six, three, eleven, six, five, thirteen and eleven wavelengths for discriminating random leaves of the four species, dorsal and ventral surfaces of A. alba, A. marina, R. mucronata, S. caseolaris, upper leaf surfaces of all the species, lower leaf surfaces, respectively. Factor analysis was used as an added tool to identify the wavelengths that were uncorrelated and contained maximum information in the combination of selected wavelengths. The results confirmed the unique spectral signatures of the four species, which could be explained in terms of leaf properties unique to the species. Cellular structure and pigmentation of the isolateral leaves of S. caseolaris are very different from the dorsiventral ones of the other three, which significantly changed the reflectance characteristics of the species.

결정질 실리콘 태양전지의 Ag 촉매층을 이용한 나노 텍스쳐링 공정에 관한 연구

In our report a relatively simple process for fast nano-texturing of p-type(100) CZ- silicon surface using silver catalyzed wet chemical etching in aqueous hydrofluoric acid (HF) and hydrogen peroxide solution(<TEX>$H_2O_2$</TEX>) at room temperature. The wafers were saw-damaged by NaOH(6 wt%) at <TEX>$60^{\circ}C$</TEX> for 150s. To obtain a nano-structured black surface, a thin layer of silver with thickness of 1 - 10 nm was deposited on the surfaces by evaporation system. After this process the samples were etched in HF : <TEX>$H_2O_2$</TEX> : <TEX>$H_2O$</TEX> = 1:5:10 at room temperature for 80s - 220s. Due to the local catalytic of the Ag clusters, this treatment results in the nano-scale texturing on the surface. This resulted in average reflectance values less than 9% after the silver on the surface of the wafers were removed.

Robustness of analyses of imaging data

Successful classifications of reflectance and vibrational data are to a large extent dependent upon robustness of input data. In this study, a well-known geostatistical approach, variogram analysis, was described and its robustness was assessed through comprehensive evaluation of 3,200 variogram settings. High-resolution hyperspectral imaging data were acquired from greenhouse maize plants, and the robustness (radiometric repeatability) of three variogram parameters (nugget, sill, and range) was examined when generated from imaging data collected from two different sets of plants and with imaging data collected on seven different days in two years. Robustness of variogram parameters was compared with average reflectance values in six spectral bands, three standard vegetation indices (NDVI, SI, and PRI), and PCA scores from principal component analysis.

Terahertz spectroscopic imaging of a rabbit VX2 hepatoma model

Terahertz (THz) spectroscopic imaging technique was applied to classify the tumor region in the rabbit liver with VX2 hepatocellular carcinoma. Within the measurement range of 0.1–2 THz, the average reflectance values for all tumor samples were more than 4% higher than those for healthy cells, and the terahertz measurements correlated well with histological analysis results. This study on paraffin-embedded tissues showed the alteration of cell density and protein content in tumors, excluding the effect of water.

Does Pond Water Reflectance Influence Double-crested Cormorant Selection of Aquaculture Ponds?

Double-crested cormorants, Phalacrocorax auritus, are a frequent and major avian predator on channel catfish, Ictalurus punctatus, and other aquaculture species throughout the southeastern USA. Although cormorant movements and occurrence within the aquaculture production region are understood, no studies have focused on the mechanisms utilized by these avian predators to select foraging sites within these high-density aquaculture systems. The objective of this study was to determine if cormorant abundance is associated with specific (ultraviolet to visible) light reflectance spectra within commercial catfish ponds. Three commercial farms were used in this study; each farm had four ponds classified as and another four ponds classified as based on observing cormorant numbers for 3 mo prior to reflectance measures (>100 h observation for each pond). Reflectance and pond turbidity were measured weekly for 7 wk during the period of maximal over-wintering cormorant numbers. Water samples were collected at the surface (1 cm depth) and secchi depth (10-41 cm) at two locations (upwind and downwind sides) within each pond to determine spectral reflectance and turbidity. Average pond reflectance values were not significantly different between ponds preferred and avoided by cormorants; however, upwind reflectance significantly differed from downwind reflectance between cormorant use groups. Using cross-validation discriminant analysis, the accuracy of separating upwind ponds preferred and avoided by cormorants was over 62%. Repeated measures ANOVA identified the reflectance at 370, 380, 460, 500, 510, and 620 nm as significantly different between ponds preferred and avoided by cormorants. The lower wavelengths (380-410 nm) correspond to known UV-A sensing compounds in cormorants and the other wavelengths share characteristics associated with algal biomass. Cormorants utilize ponds that have lower algal biomass when compared with avoided ponds.

Variogram Analysis of Hyperspectral Data to Characterize the Impact of Biotic and Abiotic Stress of Maize Plants and to Estimate Biofuel Potential

A considerable challenge in applied agricultural use of reflection-based spectroscopy is that most analytical approaches are quite sensitive to radiometric noise and/or low radiometric repeatability. In this study, hyperspectral imaging data were acquired from individual maize leaves and the main objective was to evaluate a classification system for detection of drought stress levels and spider mite infestation levels across maize hybrids and vertical position of maize leaves. A second objective was to estimate biomass and biofuel potential (heating value) of growing maize plants. Stepwise discriminant analysis was used to identify the five spectral bands (440, 462, 652, 706, and 784 nm) that contributed most to the classification of three levels of drought stress (moderate, subtle, and none) across hybrids, leaf position, and spider mite infestation. Regarding the five selected spectral bands, average reflectance values and standard variogram parameters ("nugget", "sill", and "range" derived from variogram analysis) were examined as indicators of spider mite and/or drought stress. There was consistent significant effect of drought stress on average reflectance values, while only one spectral band responded significantly to spider mite infestations. Different variogram parameters provided reliable indications of spider mite infestation and drought stress. Based on independent validation, variogram parameters could be used to accurately predict spider mite density but were less effective as indicators of drought stress. In addition, variogram parameters were used as explanatory variables to predict biomass and biofuel potential of individual maize plants. The potential of using variogram analysis as part of hyperspectral imaging analysis is discussed.

Plasma texturing for silicon solar cells: From pyramids to inverted pyramids-like structures

We have studied systematically a dry and free mask texturing process of crystalline silicon wafers using SF 6/O 2 plasmas in a reactive ion etching (RIE) system, with special attention on the effect of the RF plasma power and the SF 6/O 2 ratio on the texture of the silicon surface. In particular, we have found that by increasing the RF power, with an optimized SF 6/O 2 ratio and pressure it is possible to switch from a random texture, to a pyramid-like texture and finally to an inverted pyramid-like texture. This resulted in average reflectance values as low as 6%, which open an exciting opportunity for crystalline silicon solar cells applications.

Estimation of citrus yield from canopy spectral features determined by airborne hyperspectral imagery

Hyperspectral imagery has become increasingly available in recent years and this has necessitated the evaluation of its potential for crop monitoring and precision agriculture applications. The potential of using airborne hyperspectral imagery to develop yield prediction models for citrus fruits was examined in this paper. Hyperspectral images in 72 visible and near-infrared (NIR) wavelengths (407–898 nm) were acquired over a citrus orchard in Japan by an Airborne Imaging Spectrometer for Applications (AISA) Eagle system. The canopy spectral features of individual trees were identified using pixel-based average spectral reflectance values at various wavelengths from the acquired images, which were then used to develop yield prediction models. Yield prediction models were developed using three different techniques: (i) three commonly employed vegetation indices, i.e. the normalized difference vegetation index (NDVI), simple ratio (SR) and photochemical reflectance index (PRI); (ii) a few significant wavelengths; and (iii) partial least squares (PLS) regression factors. Greater prediction accuracy was obtained with PLS models than with the models based on NDVI, SR or PRI, or the significant wavelengths. PLS models showed a significant correlation between hyperspectral imagery data and actual citrus yield for data acquired in 2003 and 2004. These results confirmed the hypothesized correlation between canopy spectral features and citrus yield. This information is valuable for forecasting yields, planning harvest schedules and generating prescription maps for the application of tree-specific alternate bearing control measures and management practices.

Continuous Monitoring of Visible and Near-Infrared Band Reflectance from a Rice Paddy for Determining Nitrogen Uptake Using Digital Cameras

A two-band digital imaging system —one band for the visible red band (RED, 630−670 nm) and the other for the near infrared band (NIR, 820−900 nm)— was devised and positioned at a height of 12 m above a rice field of 300 m2 in area during the 2007 growing season. The imaging system automatically logged bird’seye view images at 10-min intervals from 0800−1600 every day. Radiometric corrections for the pairs of two-band images were done using solar irradiance sensors and preceding calibrations to calculate daily band-reflectance and the normalized difference vegetation index (NDVI) values for 9 plots of rice plants, with 3 levels of planting density and basal fertilization. The daily- averaged reflectance values in the RED and the NIR bands showed different but smooth seasonal changing patterns according to the growth of plants. At the maximum tiller number and the panicle formation stages, the RED and NIR reflectance values had correlation coefficients (r) of 0.79 and 0.81 with above-ground nitrogen absorption per unit land area (NA, g m-2), respectively, whereas the NDVI using the two band reflectance values showed r-value of -0.13. An empirically derived equation for the NA using two band reflectance values showed r-value of 0.96 and a root mean square of error (RMSE) 0.5 g m–2 (10% of the mean observed NA) in the estimation for the original (not validated) data set acquired at the maximum tiller number and the panicle formation stages. The results indicated that reflectance observation in the RED and NIR bands using the digital imaging system was potentially effective for assessing rice growth.

Hyperspectral imaging for nondestructive determination of internal qualities for oil palm (Elaeis guineensis Jacq. var. tenera)

The goal of this study is to develop an approach to determine the internal qualities in oil palm (Elaeis guineensis Jacq. var. tenera). Bunches and fruits belonging to 4 classes of ripeness (overripe, ripe, underripe and unripe) were used for this study. For these bunches, three of internal qualities as ripeness, oil content and free fatty acid content were examined. Since the estimation of internal qualities based on the overall data for a bunch was difficult, we focused on the average reflectance and the average relative reflectance values of fruits that were not concealed by fronds in bunch. By our approach, it was necessary to estimate the ripeness of the bunch before the oil content and free fatty acid content were determined. To classify ripeness of a bunch, the average relative reflectance values of bunches in different classes of ripeness were used and classified based on Euclidean distance. In addition, ratio of chlorophyll to carotenoids (Rp) was also used for estimating ripeness of a bunch. Then oil content (OC) and free fatty acid (FFA) content were predicted by calibration models corresponding to the class of ripeness. Correct estimation results in all classes of ripeness were obtained by both methods. The coefficients of determination (R2) were 99.7% and 99.5% with a standard error of prediction (SEP) of 0.421 and 0.190 in the validation of oil content and free fatty acid models, respectively. For oil palm fruits, methods to estimate the ripeness of the fruits were developed. Ripeness estimation using the average relative reflectance values in lower part of the fruit was compared with ripeness estimation using the ratio of a not-pale greenish yellow area, a not-yellow area and a not-reddish orange area to the entire area of fruit. The correct estimation in all classes of ripeness was obtained by using the average relative reflectance at lower part of fruit while a correct ripeness estimation rate of 97.92% was gained by using ratio of area in fruit. Since the ripeness estimation using the ratio of the area of the fruits can be done automatically, it may provide more practically applicable for the assessment of fruit ripeness in the factory.

Spectral characteristics of plant communities from salt marshes: A case study from Chongming Dongtan, Yangtze estuary, China

The spectral reflectance of recently formed salt marshes at the mouth of the Yangtze River, which are undergoing invasion by Spartina alterniflora, were assessed to determine the potential utility of remotely sensed data in assessing future invasion and changes in species composition. Following a review of published research on remote sensing of salt marshes, 53 locations along three transects were sampled for paired data on plant species composition and spectral reflectance using a FieldSpec™ Pro JR Field Portable Spectroradiometer. Spectral data were processed concerning reflectance, and the averaged reflectance values for each sample were reanalysed to correspond to a 12-waveband bandset of the Compact Airborne Spectral Imager. The spectral data were summarised using principal components analysis (PCA) and the relationships between the vegetation composition, and the PCA axes of spectral data were examined. The first PCA axis of the reflectance data showed a strong correlation with variability in near infrared reflectance and ‘brightness’, while the second axis was correlated with visible reflectance and ‘greenness’. Total vegetation cover, vegetation height, and mudflat cover were all significantly related to the first axis. The implications of this in terms of the ability of remote sensing to distinguish the various salt marsh species and in particular the invasive species S. alterniflora were discussed. Major differences in species with various physiognomies could be recognised but problems occurred in separating early colonising S. alterniflora from other species at that stage. Further work using multi-seasonal hyperspectral data might assist in solving these problems.

Potential of airborne hyperspectral imagery to estimate fruit yield in citrus

Alternate bearing is a well-marked yield variability phenomenon that occurs in almost all tree-fruit crops. The potential benefits of applying various alternate bearing control measures on alternate bearing crops can only be realized when yield information on individual trees of particular crops is obtained. The objective of this study was to examine the potential of airborne hyperspectral imagery to estimate the fruit yield in citrus. Hyperspectral images in 72 visible and near-infrared (NIR) wavelengths (from 407 to 898 nm) were acquired over a citrus orchard in Japan by an Airborne Imaging Spectrometer for Applications (AISA) Eagle system. The canopy features of individual trees were identified using pixel-based average spectral reflectance values at various wavelengths from the acquired images, which were then used to develop yield prediction models. Yield prediction models were developed using five different techniques — (i) several vegetation indices (VIs), (ii) key wavelengths determined by simple correlation analysis (SCA), (iii) principal components (PCs) based on principal component regression (PCR), and (iv) PLS factors as well as (v) important wavelengths determined by B-matrix based on partial least squares (PLS) regression. The results indicated that the VIs used in this study were poorly correlated with fruit yield on individual trees. The key or important wavelengths determined by the two methods proposed in this study could provide reasonable prediction of fruit yield. Comparatively, the B-matrix method based on the PLS regression was superior to the simple correlation analysis in determining the key or importance wavelengths that are correlated to the fruit yield. However, the PCs extracted from the hyperspectral data were weak predictors of citrus yield. Greater prediction accuracy was obtained with the model based on PLS factors than with the models based on the key or important wavelengths. These results confirmed the hypothesized correlation between canopy features and citrus yield. The methods proposed in this study have considerable promise in estimating fruit yield on individual citrus trees. The yield information is valuable for planning harvest schedules and developing programs for application of tree-specific alternate bearing control measures and other management practices.