CIMES: A package of programs for determining canopy geometry and solar radiation regimes through hemispherical photographs

Gonsamo, Alemu; Walter, Jean-Michel N.; Pellikka, Petri

doi:10.1016/j.compag.2011.10.001

Cited by 65 publications

(52 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Due to the feature of analysing images with a constant threshold value, not only is the EC method easy to carry out, but most importantly, its estimation accuracy is independent of operators' training. Many HP programs, especially free programs (e.g., gap light analyzer (GLA; Frazer et al 1999) and CIMES (Gonsamo et al 2011)), cannot perform an auto-thresholding function, which means that extra time and effort are needed to carry out autothresholding processes with different programs. On the other hand, most programs can threshold through assigning a specific threshold value, indicating that the operation of the EC method can be easily incorporated into these programs.…”

Section: Application Of Exposure and Thresholding Methodsmentioning

confidence: 99%

“…For most established image-analysis programs of hemispherical photography (HP), every image pixel has to be classified into either sky (completely white) or canopy (completely black) pixels before any image analysis, because HP estimations are performed through analysing the distribution of black and white pixels in canopy hemispherical photographs (CHPs) (e.g., Frazer et al 1999;Gonsamo et al 2011). Although ideally sky pixels in CHPs look white and canopy pixels look black, greyness of both sky and canopy pixels varies considerably (Zhang et al 2005).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Improving accuracy of canopy hemispherical photography by a constant threshold value derived from an unobscured overcast sky

et al. 2014

View full text Add to dashboard Cite

High image discrimination threshold values tend to be given to canopy hemispherical photographs (CHPs) with high exposure (resulting in bright images), but the effects of exposure on image threshold have been overlooked. A model canopy system was developed to precisely manipulate exposure (in relation to reference exposure measured from an unobscured overcast model sky), canopy openness, gap fragmentation and sky illumination of CHPs. We showed that there was a numerical trade-off relationship between exposure and image threshold of CHPs, whereas the last three factors had negligible effects on image threshold. A new thresholding method based on this relationship was shown to be applicable in the field and to allow users of hemispherical photography (HP) to compensate for the effects of higher exposure on CHPs with higher empirical threshold values. The advantages of this method are as follows: (i) it is an objective method; (ii) its overall performance is better than that of automatic thresholding methods throughout a wide range of canopy openness and exposure; and (iii) its efficiency of image analysis is higher than that of conventional manual and automatic thresholding methods, because all CHPs can be analysed with a constant empirical threshold value. Our results highlight the necessity of integrating both exposure and thresholding for optimal CHP results and the contribution that model canopies can make to methodological studies of HP.Résumé : Des valeurs élevées de seuil de mobilité de l'image ont tendance à être attribuées aux photographies hémisphériques du couvert forestier (PHCF) avec un long temps de pose. Cela produit des images lumineuses mais on ne s'est pas préoccupé des effets du temps de pose sur le seuil de l'image. Un système de modélisation du couvert forestier a été développé pour manipuler avec précision le temps de pose (en relation avec un temps de pose de référence mesuré à partir de la modélisation d'un ciel couvert non obstrué), l'ouverture du couvert forestier, la fragmentation due aux trouées et l'éclairage du ciel des PHCF. Nous avons montré qu'il y avait une relation de compensation numérique entre le temps de pose et le seuil de l'image des PHCF tandis que les trois derniers facteurs avaient des effets négligeables sur le seuil de l'image. Nous avons aussi démontré qu'une nouvelle méthode de seuillage fondée sur cette relation était applicable sur le terrain et permettait aux utilisateurs de la photographie hémisphérique (PH) de compenser les effets d'un plus long temps de pose sur les PHCF par des valeurs empiriques de seuil plus élevées. Les avantages de cette méthode sont : (i) l'objectivité de la méthode, (ii) une performance globale meilleure que celle des méthodes d'autoseuillage pour une large gamme d'ouvertures du couvert forestier et de temps de pose, et (iii) une analyse de l'image plus efficace que celle des méthodes de seuillage manuelles ou automatiques conventionnelles parce que toutes les PHCF peuvent être analysées avec une valeur de seuil empirique constante. Nos ...

show abstract

Section: Application Of Exposure and Thresholding Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving accuracy of canopy hemispherical photography by a constant threshold value derived from an unobscured overcast sky

et al. 2014

View full text Add to dashboard Cite

show abstract

“…The total GF was calculated with the CLMPML program of the CIMES package [6] and with image area between 30 • and 60 • zenith angle [21]. To compare between the estimated and reference GF at the segment level, we used the GFA program of CIMES.…”

Section: Methodsmentioning

confidence: 99%

“…The importance of GF data is that they allow estimating other canopy structural characteristics indirectly [6]. Canopy gaps refer to spaces in the canopy that could be pierced with a thin rectilinear probe (or light beam) without any contact with plant elements until reaching a point on the ground [7], [8].…”

Section: Introductionmentioning

confidence: 99%

Enhanced Gap Fraction Extraction From Hemispherical Photography

Díaz

Lencinas

2015

IEEE Geosci. Remote Sensing Lett.

View full text Add to dashboard Cite

Canopy structure can be estimated using gap fraction (GF) data, which can be directly measured with hemispherical photography. However, GF data accuracy is affected by sunlit canopy, multiple scattering, vignetting, blooming, and chromatic aberration. Here, we present an algorithm to classify hemispherical photography, whose aim is to reduce errors in the extraction of GF data. The algorithm, which was implemented in free software, uses color transformations, fuzzy logic, and object-based image analysis. The results suggest that color and texture, rather than only brightness, can be used to extract GF data.Index Terms-Fish-eye photography, forestry, fuzzy logic, image classification, image texture analysis. 1545-598X

show abstract

“…A widely used program package for DHP named "CIMES" was adopted to calculate the leveled gap fraction distribution [18]. The solar radiation regimes and canopy structure attributes can be determined from the DHP images using this software.…”

Section: B Design Of Numerical Experimentsmentioning

confidence: 99%

Comparison of Five Slope Correction Methods for Leaf Area Index Estimation From Hemispherical Photography

Cao

et al. 2015

IEEE Geosci. Remote Sensing Lett.

View full text Add to dashboard Cite

We compare five slope correction methods developed by Walter et al., Montes et al., Schleppi et al., España et al., and Gonsamo et al. (referred to as WAL, MON, SCH, ESP, and GON, respectively) using artificial fisheye pictures simulated by graphics software and a lookup table (LUT) retrieval method. The LUT is built by simulating the directional gap fraction as a function of leaf area index (LAI) and average leaf inclination angle (ALIA) using the Poisson law. LAI and ALIA estimates correspond to the case of the LUT that provides the lowest root-mean-square error between the observed gap fractions after slope correction and the simulated ones. Three LAI values (1.5, 3.5, and 5.5), four ALIA values (26.8 • , 45 • , 57.5 • , and 63.2 • ), and three slope angles (0 • , 20 • , and 50 • ) constituted 36 samples of random scenes. ESP is recommended because its results are accurate and independent on the leaf angle distribution (LAD), while GON only performs well for spherical LAD. The three other methods present less good performances with underestimation or overestimation of LAI and/or ALIA depending on the LAD, and the recommended order for them is MON, SCH, and WAL. Index Terms-Average leaf inclination angle (ALIA), digital hemispherical photography (DHP), leaf area index (LAI), slope correction, topographic mask.Manuscript

show abstract

CIMES: A package of programs for determining canopy geometry and solar radiation regimes through hemispherical photographs

Cited by 65 publications

References 36 publications

Improving accuracy of canopy hemispherical photography by a constant threshold value derived from an unobscured overcast sky

Improving accuracy of canopy hemispherical photography by a constant threshold value derived from an unobscured overcast sky

Enhanced Gap Fraction Extraction From Hemispherical Photography

Comparison of Five Slope Correction Methods for Leaf Area Index Estimation From Hemispherical Photography

Contact Info

Product

Resources

About