The effect of free water in a maize canopy on microwave emission at 1.4 GHz

Brian K. Hornbuckle, Anthony W. England, Martha C. Anderson, Brian James Viner

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Free water in a maize canopy has the net effect of decreasing the brightness temperature at 1.4 GHz (wavelength of 21 cm). It appears that only one form of free water, dew, causes this decrease in brightness temperature. It is not clear how the other form of free water, intercepted precipitation, effects the brightness temperature. This effect occurs at both polarizations, but vertically polarized brightness is affected more than horizontally polarized brightness. We observed a decrease in the horizontally polarized and vertically polarized brightness temperature of a maize canopy of 2 and 4 K, respectively, when intercepted precipitation and dew were present. Since free water in the canopy has been observed to increase the brightness temperature of wheat and grass at 1.4 GHz, we hypothesize that the effect of free water on terrestrial microwave emission depends on the physical dimensions of vegetation canopy components (such as stems, leaves, and fruit) relative to the wavelength of observation. Free water on vegetation will increase terrestrial microwave emission when vegetation canopy components are electrically small, and decrease terrestrial microwave emission when the sizes of some vegetation canopy components are comparable to the observing wavelength and hence scattering in the canopy is significant, as in the case of maize. The electrical size of vegetation components therefore determines the relative enhancement of emission and scattering by free water in the canopy. The most widely used model of microwave emission does not account for the effect of free water on vegetation. Bias introduced by the presence of free water could be a significant source of error in retrieved soil moisture from future 1.4 GHz satellite radiometers.

Original languageEnglish (US)
Pages (from-to)180-191
Number of pages12
JournalAgricultural and Forest Meteorology
Volume138
Issue number1-4
DOIs
StatePublished - Aug 29 2006
Externally publishedYes

Fingerprint

maize
canopy
corn
brightness temperature
water
vegetation
wavelengths
dew
temperature
wavelength
scattering
effect
microwave
radiometers
radiometer
polarization
fruit
soil moisture
wheat
stem

Keywords

  • Dew
  • Micrometeorology
  • Remote sensing
  • Soil moisture
  • Surface energy balance
  • Vegetation

ASJC Scopus subject areas

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science

Cite this

The effect of free water in a maize canopy on microwave emission at 1.4 GHz. / Hornbuckle, Brian K.; England, Anthony W.; Anderson, Martha C.; Viner, Brian James.

In: Agricultural and Forest Meteorology, Vol. 138, No. 1-4, 29.08.2006, p. 180-191.

Research output: Contribution to journalArticle

Hornbuckle, Brian K. ; England, Anthony W. ; Anderson, Martha C. ; Viner, Brian James. / The effect of free water in a maize canopy on microwave emission at 1.4 GHz. In: Agricultural and Forest Meteorology. 2006 ; Vol. 138, No. 1-4. pp. 180-191.
@article{d2e98aad48de41b4a9808c0ce0513166,
title = "The effect of free water in a maize canopy on microwave emission at 1.4 GHz",
abstract = "Free water in a maize canopy has the net effect of decreasing the brightness temperature at 1.4 GHz (wavelength of 21 cm). It appears that only one form of free water, dew, causes this decrease in brightness temperature. It is not clear how the other form of free water, intercepted precipitation, effects the brightness temperature. This effect occurs at both polarizations, but vertically polarized brightness is affected more than horizontally polarized brightness. We observed a decrease in the horizontally polarized and vertically polarized brightness temperature of a maize canopy of 2 and 4 K, respectively, when intercepted precipitation and dew were present. Since free water in the canopy has been observed to increase the brightness temperature of wheat and grass at 1.4 GHz, we hypothesize that the effect of free water on terrestrial microwave emission depends on the physical dimensions of vegetation canopy components (such as stems, leaves, and fruit) relative to the wavelength of observation. Free water on vegetation will increase terrestrial microwave emission when vegetation canopy components are electrically small, and decrease terrestrial microwave emission when the sizes of some vegetation canopy components are comparable to the observing wavelength and hence scattering in the canopy is significant, as in the case of maize. The electrical size of vegetation components therefore determines the relative enhancement of emission and scattering by free water in the canopy. The most widely used model of microwave emission does not account for the effect of free water on vegetation. Bias introduced by the presence of free water could be a significant source of error in retrieved soil moisture from future 1.4 GHz satellite radiometers.",
keywords = "Dew, Micrometeorology, Remote sensing, Soil moisture, Surface energy balance, Vegetation",
author = "Hornbuckle, {Brian K.} and England, {Anthony W.} and Anderson, {Martha C.} and Viner, {Brian James}",
year = "2006",
month = "8",
day = "29",
doi = "10.1016/j.agrformet.2006.05.003",
language = "English (US)",
volume = "138",
pages = "180--191",
journal = "Agricultural and Forest Meteorology",
issn = "0168-1923",
publisher = "Elsevier",
number = "1-4",

}

TY - JOUR

T1 - The effect of free water in a maize canopy on microwave emission at 1.4 GHz

AU - Hornbuckle, Brian K.

AU - England, Anthony W.

AU - Anderson, Martha C.

AU - Viner, Brian James

PY - 2006/8/29

Y1 - 2006/8/29

N2 - Free water in a maize canopy has the net effect of decreasing the brightness temperature at 1.4 GHz (wavelength of 21 cm). It appears that only one form of free water, dew, causes this decrease in brightness temperature. It is not clear how the other form of free water, intercepted precipitation, effects the brightness temperature. This effect occurs at both polarizations, but vertically polarized brightness is affected more than horizontally polarized brightness. We observed a decrease in the horizontally polarized and vertically polarized brightness temperature of a maize canopy of 2 and 4 K, respectively, when intercepted precipitation and dew were present. Since free water in the canopy has been observed to increase the brightness temperature of wheat and grass at 1.4 GHz, we hypothesize that the effect of free water on terrestrial microwave emission depends on the physical dimensions of vegetation canopy components (such as stems, leaves, and fruit) relative to the wavelength of observation. Free water on vegetation will increase terrestrial microwave emission when vegetation canopy components are electrically small, and decrease terrestrial microwave emission when the sizes of some vegetation canopy components are comparable to the observing wavelength and hence scattering in the canopy is significant, as in the case of maize. The electrical size of vegetation components therefore determines the relative enhancement of emission and scattering by free water in the canopy. The most widely used model of microwave emission does not account for the effect of free water on vegetation. Bias introduced by the presence of free water could be a significant source of error in retrieved soil moisture from future 1.4 GHz satellite radiometers.

AB - Free water in a maize canopy has the net effect of decreasing the brightness temperature at 1.4 GHz (wavelength of 21 cm). It appears that only one form of free water, dew, causes this decrease in brightness temperature. It is not clear how the other form of free water, intercepted precipitation, effects the brightness temperature. This effect occurs at both polarizations, but vertically polarized brightness is affected more than horizontally polarized brightness. We observed a decrease in the horizontally polarized and vertically polarized brightness temperature of a maize canopy of 2 and 4 K, respectively, when intercepted precipitation and dew were present. Since free water in the canopy has been observed to increase the brightness temperature of wheat and grass at 1.4 GHz, we hypothesize that the effect of free water on terrestrial microwave emission depends on the physical dimensions of vegetation canopy components (such as stems, leaves, and fruit) relative to the wavelength of observation. Free water on vegetation will increase terrestrial microwave emission when vegetation canopy components are electrically small, and decrease terrestrial microwave emission when the sizes of some vegetation canopy components are comparable to the observing wavelength and hence scattering in the canopy is significant, as in the case of maize. The electrical size of vegetation components therefore determines the relative enhancement of emission and scattering by free water in the canopy. The most widely used model of microwave emission does not account for the effect of free water on vegetation. Bias introduced by the presence of free water could be a significant source of error in retrieved soil moisture from future 1.4 GHz satellite radiometers.

KW - Dew

KW - Micrometeorology

KW - Remote sensing

KW - Soil moisture

KW - Surface energy balance

KW - Vegetation

UR - http://www.scopus.com/inward/record.url?scp=33746891575&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33746891575&partnerID=8YFLogxK

U2 - 10.1016/j.agrformet.2006.05.003

DO - 10.1016/j.agrformet.2006.05.003

M3 - Article

AN - SCOPUS:33746891575

VL - 138

SP - 180

EP - 191

JO - Agricultural and Forest Meteorology

JF - Agricultural and Forest Meteorology

SN - 0168-1923

IS - 1-4

ER -