Relating the X-band opacity of a tropical tree canopy to sapflow, rain interception and dew formation

During summer and autumn 2007, a 11 GHz microwave radiometer was deployed in an experimental tree plantation in Sardinilla, Panama. The opacity of the tree canopy was derived from incoming brightness temperatures received on the ground. A collocated eddy-covariance flux tower measured water vapor fluxes and meteorological variables above the canopy. In addition, xylem sapflow of trees was measured within the flux tower footprint. We observed considerable diurnal differences between measured canopy opacities and modeled theoretical opacities that were closely linked to xylem sapflow. It is speculated that dielectric changes in the leaves induced by the sapflow are causing the observed diurnal changes. In addition, canopy intercepted rain and dew formation also modulated the diurnal opacity cycle. With an enhanced canopy opacity model accounting for water deposited on the leaves, we quantified the influence of canopy stored water (i.e. intercepted water and dew) on the opacity. A time series of dew formation and rain interception was directly monitored during a period of two weeks. We found that during light rainfall up to 60% of the rain amount is intercepted by the canopy whereas during periods of intense rainfall only 4% were intercepted. On average, 0.17 mm of dew was formed during the night. Dew evaporation contributed 5% to the total water vapor flux measured above the canopy.

[1]  Willem Bouten,et al.  Monitoring and modelling canopy water storage amounts in support of atmospheric deposition studies , 1996 .

[2]  Amalia E. Barrios.  Propagation Modeling , 2012 .

[3]  F. Valente,et al.  Modelling interception loss for two sparse eucalypt and pine forests in central Portugal using reformulated Rutter and Gash analytical models , 1997 .

[4]  Paul Holiday,et al.  Fungus diseases of tropical crops , 1980, Australasian Plant Pathology.

[5]  P. Rosenkranz.  Water vapor microwave continuum absorption: A comparison of measurements and models , 1998 .

[6]  P. Dutilleul,et al.  Neighborhood effects and size-asymmetric competition in a tree plantation varying in diversity. , 2009, Ecology.

[7]  L. Schwendenmann,et al.  Seasonal dynamics of tree sap flux and water use in nine species in Panamanian forest plantations , 2010 .

[8]  Thomas Meissner,et al.  The complex dielectric constant of pure and sea water from microwave satellite observations , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[9]  M. Janssen.  Atmospheric Remote Sensing by Microwave Radiometry , 1993 .

[10]  Alexander A. Chukhlantsev,et al.  Microwave radiometry of vegetation canopies , 2006 .

[11]  Yong Han,et al.  Analysis and improvement of tipping calibration for ground-based microwave radiometers , 2000, IEEE Trans. Geosci. Remote. Sens..

[12]  Willem Bouten,et al.  Microwave transmission, a new tool in forest hydrological research , 1991 .

[13]  Kyle McDonald,et al.  Diurnal change in trees as observed by optical and microwave sensors: the EOS synergism study , 1991, IEEE Trans. Geosci. Remote. Sens..

[14]  D. Fitzjarrald,et al.  Detecting rainfall interception in an Amazonian rain forest with eddy flux measurements. , 2009 .

[15]  Marco A. Janssen.  An Introduction to the Passive Microwave Remote Sensing of Atmospheres , 1993 .

[16]  A. Granier.  Une nouvelle méthode pour la mesure du flux de sève brute dans le tronc des arbres , 1985 .

[17]  Paolo Pampaloni,et al.  Microwave radiometry of forests , 2004 .

[18]  A. Granier,et al.  Evaluation of transpiration in a Douglas-fir stand by means of sap flow measurements. , 1987, Tree physiology.

[19]  S. Dekker,et al.  Identification of rainfall interception model parameters from measurements of throughfall and forest canopy storage , 2003 .

[20]  G. Kidron,et al.  Microclimate control upon sand microbiotic crusts, western Negev Desert, Israel , 2000 .

[21]  Peter E. Thornton,et al.  The Partitioning of Evapotranspiration into Transpiration, Soil Evaporation, and Canopy Evaporation in a GCM: Impacts on Land–Atmosphere Interaction , 2007 .

[22]  J. P. Kimmins.  Some Statistical Aspects of Sampling Throughfall Precipitation in Nutrient Cycling Studies in British Columbian Coastal Forests , 1973 .

[23]  Jin Au Kong,et al.  Theory of electromagnetic waves , 1975 .

[24]  J. A. Vozzo.  Tropical tree seed manual. , 2002 .

[25]  H. Hanado,et al.  Diurnal change of Amazon rain forest /spl sigma//sup 0/ observed by Ku-band spaceborne radar , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[26]  Brent Clothier,et al.  ESTIMATION OF SOIL HEAT FLUX FROM NET RADIATION DURING THE GROWTH OF ALFALFA , 1986 .

[27]  Jan Vanderborght,et al.  Measured microwave radiative transfer properties of a deciduous forest canopy , 2007 .

[28]  Nurit Agam,et al.  Dew formation and water vapor adsorption in semi-arid environments : A review , 2006 .

[29]  N. Agama,et al.  Dew formation and water vapor adsorption in semi-arid environments — A review , 2006 .

[30]  Jean-Pierre Wigneron,et al.  Modeling Forest Emissivity at L-Band and a Comparison With Multitemporal Measurements , 2007, IEEE Geoscience and Remote Sensing Letters.

[31]  Paolo Ferrazzoli,et al.  Passive microwave remote sensing of forests: a model investigation , 1996, IEEE Trans. Geosci. Remote. Sens..

[32]  Paolo Ferrazzoli,et al.  Passive Microwave Remote Sensing of Forests , 1996 .

[33]  J. Testud,et al.  Rainfall spatial variability observed by X-band weather radar and its implication for the accuracy of rainfall estimates , 2009 .

[34]  Walter Senn,et al.  A cospectral correction model for measurement of turbulent NO2 flux , 1995 .

[35]  Fawwaz T. Ulaby,et al.  Microwave dielectric behavior of vegetation material , 1987 .

[36]  Christian Mätzler,et al.  Microwave (1-100 GHz) dielectric model of leaves , 1994, IEEE Trans. Geosci. Remote. Sens..

[37]  David M. Le Vine,et al.  A microwave polarimetric scattering model for forest canopies based on vector radiative transfer theory , 1995 .

[38]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .

[39]  Emanuele Santi,et al.  Ground-based microwave investigations of forest plots in Italy , 2007, 2007 IEEE International Geoscience and Remote Sensing Symposium.

[40]  Yann Kerr,et al.  Passive microwave remote sensing of land-atmosphere interactions , 1995 .

[41]  Christian Mätzler,et al.  Microwave transmissivity of a forest canopy: Experiments made with a beech , 1994 .

[42]  D. Pozar,et al.  Theory of electromagnetic waves , 1984, IEEE Antennas and Propagation Society Newsletter.

[43]  A. Granier,et al.  A new method of sap flow measurement in tree stems , 1985 .

[44]  Robert J. Nicholls,et al.  Monitoring and Modelling , 1985 .

[45]  Hans J. Liebe,et al.  Propagation Modeling of Moist Air and Suspended Water/Ice Particles at Frequencies Below 1000 GHz , 1993 .

[46]  C. Simmer,et al.  Interpretation of Polarization Features in Ground-Based Microwave Observations as Caused by Horizontally Aligned Oblate Raindrops , 2001 .

[47]  M. Penka,et al.  Water potential and sap flow rate in adult trees with moist and dry soil as used for the assessment of root system depth , 2008, Biologia Plantarum.

[48]  E. K. Webb,et al.  Correction of flux measurements for density effects due to heat and water vapour transfer , 1980 .

[49]  Michael Bass,et al.  Handbook of optics , 1995 .

[50]  R. E. Ruskin,et al.  Humidity and Moisture , 1966 .

[51]  Thomas J. Jackson,et al.  L-Band Radar Estimation of Forest Attenuation for Active/Passive Soil Moisture Inversion , 2009, IEEE Transactions on Geoscience and Remote Sensing.

[52]  P. Derfler,et al.  The United States Department of Agriculture , 1872, Nature.

[53]  Michael H. Cosh,et al.  Dew frequency, duration, amount, and distribution in corn and soybean during SMEX05 , 2008 .

[54]  Mike Schwank,et al.  Testing a New Model for the L-Band Radiation of Moist Leaf Litter , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[55]  R. Jeu,et al.  Global canopy interception from satellite observations , 2010 .

[56]  K.C. McDonald,et al.  Diurnal and spatial variation of xylem dielectric constant in Norway Spruce (Picea abies [L.] Karst.) as related to microclimate, xylem sap flow, and xylem chemistry , 2002, IEEE Trans. Geosci. Remote. Sens..

[57]  W. Eugster,et al.  X-band opacity of a tropical tree canopy and its relation to intercepted rain, eddy fluxes and other meteorological variables , 2008, 2008 Microwave Radiometry and Remote Sensing of the Environment.

[58]  C. Mätzler,et al.  A radiative transfer model for an idealized and non-scattering atmosphere and its application for ground-based remote sensing , 2011 .