Thermal remote sensing from Airborne Hyperspectral Scanner data in the framework of the SPARC and SEN2FLEX projects: an overview

The AHS (Airborne Hyperspectral Scanner) instrument has 80 spectral bands covering the visible and near infrared (VNIR), short wave infrared (SWIR), mid infrared (MIR) and thermal infrared (TIR) spectral range. The instrument is operated by Instituto Nacional de Técnica Aerospacial (INTA), and it has been involved in several field campaigns since 2004. <br><br> This paper presents an overview of the work performed with the AHS thermal imagery provided in the framework of the SPARC and SEN2FLEX campaigns, carried out respectively in 2004 and 2005 over an agricultural area in Spain. The data collected in both campaigns allowed for the first time the development and testing of algorithms for land surface temperature and emissivity retrieval as well as the estimation of evapotranspiration from AHS data. Errors were found to be around 1.5 K for land surface temperature and 1 mm/day for evapotranspiration

Early Diagnosis of Vegetation Health From High-Resolution Hyperspectral and Thermal Imagery: Lessons Learned From Empirical Relationships and Radiative Transfer Modelling

[Purpose of Review] We provide a comprehensive review of the empirical and modelling approaches used to quantify the radiation–vegetation interactions related to vegetation temperature, leaf optical properties linked to pigment absorption and chlorophyll fluorescence emission, and of their capability to monitor vegetation health. Part 1 provides an overview of the main physiological indicators (PIs) applied in remote sensing to detect alterations in plant functioning linked to vegetation diseases and decline processes. Part 2 reviews the recent advances in the development of quantitative methods to assess PI through hyperspectral and thermal images.[Recent Findings] In recent years, the availability of high-resolution hyperspectral and thermal images has increased due to the extraordinary progress made in sensor technology, including the miniaturization of advanced cameras designed for unmanned aerial vehicle (UAV) systems and lightweight aircrafts. This technological revolution has contributed to the wider use of hyperspectral imaging sensors by the scientific community and industry; it has led to better modelling and understanding of the sensitivity of different ranges of the electromagnetic spectrum to detect biophysical alterations used as early warning indicators of vegetation health.[Summary] The review deals with the capability of PIs such as vegetation temperature, chlorophyll fluorescence, photosynthetic energy downregulation and photosynthetic pigments detected through remote sensing to monitor the early responses of plants to different stressors. Various methods for the detection of PI alterations have recently been proposed and validated to monitor vegetation health. The greatest challenges for the remote sensing community today are (i) the availability of high spatial, spectral and temporal resolution image data; (ii) the empirical validation of radiation–vegetation interactions; (iii) the upscaling of physiological alterations from the leaf to the canopy, mainly in complex heterogeneous vegetation landscapes; and (iv) the temporal dynamics of the PIs and the interaction between physiological changes.The authors received funding provided by the FluorFLIGHT (GGR801) Marie Curie Fellowship, the QUERCUSAT and ESPECTRAMED projects (Spanish Ministry of Economy and Competitiveness), the Academy of Finland (grants 266152, 317387) and the European Research Council Synergy grant ERC-2013-SyG-610028 IMBALANCE-P.Peer reviewe

Chlorophyll Fluorescence Detection with a High-Spectral Resolution Spectrometer through in-filling of the O2-A band as function of Water Stress in Olive Trees

2nd International Workshop on Remote Sensing of Vegetation Fluorescence, 17-19 Nov. 2004, Montreal, CanadaA high spectral resolution spectrometer of 0.065 nm FWHM in the 680-770 nm range was used for collecting spectral measurements in an orchard of olive trees in Spain under 3 different water stress treatments. The measurements were conducted as part of validation efforts for the FluorMOD project funded by the European Space Agency (ESA) to advance the science of vegetation fluorescence simulation. Diurnal steadystate chlorophyll fluorescence was measured from leaves in the field during summer 2004 using the PAM-2100 fluorometer to study the effects of water stress on chlorophyll fluorescence. Water potential, photosynthesis, and stomatal conductance on trees were also measured in a weekly basis to track the effects of water stress on the tree status and functioning. Infrared Apogee sensors were placed on top of the trees for diurnal thermal data collection, studying the effects of water stress on the tree temperature as an indicator of stress. The Ocean Optics HR-2000 spectrometer was used to measure irradiance and radiance spectra from above tree crowns under different stress conditions. The spectral measurements of irradiance with a cosine corrector and crown radiance with bare fibre were acquired from a pole 7 m in height to collect nadir radiance from the top of tree crowns. Analysis in the red edge covering the 680-770 nm range enabled the study of the chlorophyll fluorescence in-filling in the O2-A band at 760 nm. Results of the spectral analysis and simulation using the FluorMOD radiative transfer model demonstrate that water stress effects on steady-state fluorescence are detectable at the tree level in the O2-A band from reflectance spectra due to the in-filling effects.The development of the FluorMODgui interface has been carried out in the frame of the ESA-project Development of a Vegetation Fluorescence Canopy Model, ESTEC contract no. 16365/02/NL/FF. Within the same project, the leaf and canopy fluorescence models FluorMODleaf and FluorSAIL were developed and provided by R. Pedrós and S. Jacquemoud of LED, University of Paris, I. Moya, Y. Goulas and J. Louis of LURE, University of Paris-South, and Wout Verhoef, National Aerospace Laboratory NLR.Peer reviewe

Detección de Estrés Hídrico en Olivar mediante datos Hiperespectrales y Térmicos del sensor AHS

En: XI Congreso Nacional de Teledetección, Teledetección, Avances en la Observación de la Tierra, M. Arbelo, A. González, J.C. Pérez (Eds.), pág.: 53-56, Tenerife, 21-23/9/2005.El sensor hiperespectral AHS (Airborrne Hyperspectal Scanner)fue utilizado para obtener imágenesde 2.5 m de resolución espacial en el espectro visible, infrarrojo cercano y térmico en una parcela de olivar en Córdoba (España) con el fin de estudiar la variabilidad espacial y temporal del estrés hídrico. Los datos térmicos del AHS permitieron obtener imágenes detemperatura de superficie de la parcela a las 7:30,9:30 y 12:30 GMTel 25 de julio de 2004. El diseño experimental en bloques aleatorios consistió en aplicar tres dosis diferentes de riego durante julio, agosto y septiembre, realizando medidas semanales de potencial hídrico, fotosíntesis y conductancia para estudiar los efectos del estrés hídrico en el cultivo. Los sensores de infrarrojo IRT permitieron la realización de medidas continuas de temperatura sobre las copas de los árboles, facilitando la validación de las imágenes térmicas. Los resultados de este estudio son presentados, destacando la aplicabilidad en la agricultura de precisión de la teledetección térmica e hiperespectral de alta resolución espacial para el estudio del suministro y la dosificación del riego.Peer reviewe

Detection of Water Stress in Orchard Trees with a High-Resolution Spectrometer through Chlorophyll Fluorescence in-filling of the O2-A band

A high spectral resolution spectrometer with 0.065-nm full-width half-maximum was used for collecting spectral measurements in an orchard field under three water stress treatments. The study was part of the FluorMOD project funded by the European Space Agency to develop a leaf-canopy reflectance model to simulate the effects of fluorescence. Water deficit protocols generated a gradient in solar-induced chlorophyll fluorescence emission and tree physiological measures. Diurnal steady-state chlorophyll fluorescence was measured from leaves in the field between June and November 2004 using the PAM-2100 fluorometer to study the effects of water stress on chlorophyll fluorescence. Spectral measurements of downwelling irradiance and upwelling crown radiance were conducted with the narrow-band spectrometer, enabling the canopy reflectance to be obtained at subnanometer spectral resolution and permitting the evaluation of the fluorescence in-filling effects on reflectance in trees under water stress conditions. Diurnal and seasonal measurements showed consistently lower steady-state fluorescence (Ft) and quantum yield F Fm in water-stressed trees, yielding mean values of Ft = 038 (well-irrigated) and Ft = 0 21 (water-stressed trees). The agreement between Ft and water potential showed that steady-state fluorescence could be used to detect differences in water stress levels, with determination coefficients ranging between 2 = 048 and 2 = 081 for individual dates. Analysis in the 680–770-nm range showed that the chlorophyll fluorescence in-filling in the O2-A band at 760 nm is sensitive to diurnal variations of fluorescence and water stress, yielding 2 = 0 76 (well-watered treatment), 2 = 0 89 (intermediate stress treatment), and 2 = 07 (extreme stress treatment), demonstrating the close relationships between Ft and in-filling at the crown level.This work was supported in part by the Consejo Superior de Investigaciones Científicas under the CSIC-PIF Program, in part by the European Space Agency (ESA), and in part by the Spanish Ministry of Science and Technology (MCyT) for the projects PIF-200440-F035, ESA-ESTEC Contract 16365/02/NL/FF (FluorMOD), and AGL2003-01468, respectively. The work of P. J. Zarco-Tejada was supported by the Ramón y Cajal (MCyT) and Averroes (JA) programs. The work of J. R. Miller was supported by the Natural Sciences and Engineering Research Council of Canada.Peer reviewe

Grape quality assessment in vineyards affected by iron deficiency chlorosis using narrow-band physiological remote sensing indices

The present study investigated the use of physiological indices calculated from hyperspectral remote sensing imagery as potential indicators of wine grape quality assessment in vineyards affected by iron deficiency chlorosis. Different cv. Tempranillo/110 Richter vineyards located in northern Spain, affected and non-affected by iron chlorosis, were identified for field and airborne data collection. Airborne campaigns imaged a total of 14 study areas in both 2004 and 2005 using the AHS hyperspectral sensor, which acquired 20 spectral bands in the VIS-NIR region. Field measurements were conducted in each study site to obtain leaf and grape physiological parameters potentially linked to wine quality. Simulations carried out with the rowMCRM radiative transfer model demonstrated the feasibility of estimating leaf chlorophyll a+b (Cab) content using TCARI/OSAVI from AHS spectral bands. In addition to traditional structural vegetation indices (NDVI) and successful canopy-level chlorophyll indices (TCARI/OSAVI), other innovative physiological indices sensitive to changes in carotenoid (Car) and anthocyanin (Anth) content in leaves were assessed from the imagery. The rowMCRM model simulations were used to evaluate canopy structural effects on these physiological indices as a function of the typical row-structured canopy variables in vineyards (LAI, crown width, row distances, Cab content and soil background effects). Modeling results concluded that Car (Gitelson-Car2) and Anth (Gitelson-Anth) indices were highly affected by canopy structure (Cw, Vs) and soil background (ρs). Field measurements of grape composition and quality were used to assess potential relationships with physiological indices sensitive to foliar pigment content (Cab, Car and Anth). NDVI and TCARI/OSAVI indices yielded lower relationships for CIRG and IMAD must quality parameters than Car and Anth physiological indices. These results suggest that the increase in carotenes and anthocyanins due to drought, thermal damage or micronutrient deficiencies is a better indicator to detect phenolic ripening difficulties for vines affected by iron chlorosis than chlorosis detection. Therefore, the potential use of physiological remote sensing indices related to carotene and anthocyanin pigments demonstrates their importance as grape quality indicators in vineyards affected by iron chlorosis. © 2010 Elsevier Inc.This work was supported by AGL2009-13105-C03-01 grants from the Ministerio de Ciencia e Innovación (MICINN), and VA016B05 grant from the Junta de Castilla y León (Spain).Peer Reviewe

Modelling biochemical processes in orchards at leaf- and canopy-level using hyperspectral data

Presented at the Airborne Imaging Spectroscopy Workshop, BruHyp 2006, 10 October 2006, Bruges, Belgium.This research was conducted to evaluate the potential and limitations of hyperspectral remote sensing to detect iron deficiency in capital-intensive multi-annual crop systems, e.g. peach orchards. The noted deficiency can be regarded as a proxy for deviations from optimal plant functioning, while detection of such deviations is in turn of significant importance to monitoring and modelling efforts of orchards as production systems. Hyperspectral leaf, canopy, and airborne reflectance measurements were acquired in a peach (Prunus persica L.) orchard in Zaragoza, Spain. Leaf- and canopy-level data were collected with a handheld spectroradiometer (ASD, Inc.), while the AHS-160 hyperspectral sensor provided airborne data. Blocks of trees were treated with different amount of iron chelates (Sequestrene) which created a dynamic range of chlorophyll concentration as measured in leaves. Hyperspectral measurements at leaf-level were carried out to characterize the physiological aspects of nutrient stress, as opposed to the evaluation of plant nutrient status at the complete plant-level. Stressinduced physiological changes make stress detection at the leaf-level possible at an early stage of suboptimal photosynthetic functioning. Airborne imagery, however, is difficult to interpret due to altering illumination angles, BRDF effects, and intervening atmospheric light interactions resulting in an alteration of the vegetative reflectance spectrum. Although many studies have implemented hyperspectral analysis of nutrient status at large scales, this research field is still in its infancy phase, since the link between airborneand leaf-level measurements is lacking. This inevitably makes the physiological interpretation of existing hyperspectral research more complex. The multi-level (leaf, canopy, and airborne) approach presented here enabled the assessment of vegetation indices and their relationship with pigment concentration at each monitoring level. Pertinent classical chlorophyll-related vegetation indices were tested and new indices were extracted from the spectral profiles by means of band reduction techniques and narrow-waveband rationing, which involved all possible 2-band combinations. Robustness was evaluated by studying the index performance for datasets of increasing complexity, from leaf- to canopy- and airborne-level. Physiological interpretations extracted from leaf-level experiments were extrapolated to canopy- and airborne level. The measured spectra and estimated biochemical parameters were related via inversion of a linked directional homogeneous canopy reflectance model (ACRM) and the PROSPECT leaf model. Numerical model inversion was conducted by minimizing the difference between the measured reflectance samples and modelled reflectance values. An improved optimization method is presented. Results are compared with a simple linear regression analysis, linking chlorophyll to the reflectance measured at the leaf level and at the Top of Canopy (TOC), while optimal band regions and bandwidths also were analyzed.We would like to thank the Belgian Science Policy Office for financing this work.Peer reviewe

Detection of Water Stress in an Olive Orchard with Thermal Remote Sensing Imagery

An investigation of the detection of water stress in non-homogeneous crop canopies such as orchards using high-spatial resolution remote sensing thermal imagery is presented. An airborne campaign was conducted with the Airborne Hyperspectral Scanner (AHS) acquiring imagery in 38 spectral bands in the 0.43–12.5 mm spectral range at 2.5 m spatial resolution. The AHS sensor was flown at 7:30, 9:30 and 12:30 GMT in 25 July 2004 over an olive orchard with three different water-deficit irrigation treatments to study the spatial and diurnal variability of temperature as a function of water stress. A total of 10 AHS bands located within the thermal-infrared region were assessed for the retrieval of the land surface temperature using the split-window algorithm, separating pure crowns from shadows and sunlit soil pixels using the reflectance bands. Ground truth validation was conducted with infrared thermal sensors placed on top of the trees for continuous thermal data acquisition. Crown temperature (Tc), crown minus air temperature (Tc Ta), and relative temperature difference to well-irrigated trees (Tc TR, where TR is the mean temperature of the well-irrigated trees) were calculated from the ground sensors and from the AHS imagery at the crown spatial resolution. Correlation coefficients for Tc TR between ground IRT sensors and airborne image-based AHS estimations were R2 = 0.50 (7:30 GMT), R2 = 0.45 (9:30 GMT) and R2 = 0.57 (12:30 GMT). Relationships between leaf water potential and crown Tc Ta measured with the airborne sensor obtained determination coefficients of R2 = 0.62 (7:30 GMT), R2 = 0.35 (9:30 GMT) and R2 = 0.25 (12:30 GMT). Images of Tc Ta and Tc TR for the entire field were obtained at the three times during the day of the overflight, showing the spatial and temporal distribution of the thermal variability as a function of the water deficit irrigation schemes.Financial support from the Spanish Ministry of Science and Technology (MCyT) for the projects AGL2002-04407-C03 and AGL2003-01468, and financial support to P.J. Zarco-Tejada from the Ramo´n y Cajal (MCyT) and Averroes (JA) programs are gratefully acknowledged.Peer reviewe

Imaging chlorophyll fluorescence with an airborne narrow-band multispectral camera for vegetation stress detection

14 pages, 15 figures, 2 tables.-- Printed version published Jun 15, 2009.Progress in assessing the feasibility for imaging fluorescence using the O2-A band with 1 nm full-width half-maximum (FWHM) bands centered at 757.5 and 760.5 nm is reported in this paper. Multispectral airborne data was acquired at 150 m above ground level in the thermal, visible and near infrared regions yielding imagery at 15 cm spatial resolution. Simultaneous field experiments conducted in olive, peach, and orange orchards (water stress trials), and an olive orchard (variety trial) enabled the detected variability in fluorescence emission to be examined as function of stress status. In a parallel modelling activity the coupled leaf–canopy reflectance–fluorescence model, FluorMOD, was used to assess fluorescence retrieval capability by the in-filling method, as well as by fluorescence indices from the published literature. Fluorescence retrievals using the in-filling method, the derivative index D702/D680 and reflectance indices R690/R630, R761–R757, and R761/R757 yielded the best results in the simulation study, while demonstrating insensitivity to leaf area index (LAI) variation. The fluorescence in-filling method, derivative index D702/D680, and R761–R757 were the indices least affected by chlorophyll a + b (Cab) variation. On the other hand, other published indices for fluorescence detection at leaf and canopy levels exhibited high sensitivity to variations in Cab and LAI, and therefore were considered less suitable for in-field fluorescence detection. The fluorescence signal extraction from airborne imagery using the in-filling method was validated through comparisons with field-measured steady-state fluorescence (Fs) using the PAM-2100 and GFS-3000 instruments, confirming simulation predictions. The water stress experiments conducted on olive and peach orchards demonstrated the feasibility of chlorophyll fluorescence (F) extraction at the tree level from the airborne imagery, yielding determination coefficients r2 = 0.57 (olive), and r2 = 0.54 (peach). Consistent results were obtained between airborne F and ground truth assimilation (A) measured in the olive variety field experiment under no water stress levels, yielding r2 = 0.71.Financial support from the Spanish Ministry of Science and Education (MEC) for the projects AGL2005-04049, EXPLORA-INGENIO AGL2006-26038-E/AGR, and CONSOLIDER CSD2006-67, is gratefully acknowledged, as well as the Junta de Andalucía—Excelencia AGR-595, Gobierno de Aragón (A03 research group) and PETRI PET2005-0616. Technical support from the UAV Navigation and the Tetracam Inc. for the accommodation of airborne requirements are also acknowledged.Peer reviewe