A SCINTILLOMETER FOR MEASUREMENT OF SENSIBLE HEAT FLUXES ON 100 TO 10,000 M SCALES OVER HETEROGENEOUS WATERSHEDS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0196019
• Grant No.: 2003-35102-13524
• Proposal No.: 2003-01640
• Project Start Date: Aug 1, 2003
• Project End Date: Jul 31, 2004
• Grant Year: 2003
• Program Code: [26.0]- (N/A)

Recipient Organization
NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
801 LEROY PL
SOCORRO,NM 87801-4750

Performing Department
(N/A)

Non Technical Summary
Standard techniques for the measurement of the sensible heat flux (Bowen Ratio, eddy covariance) do not provide a measurement at the scale of a typical remote sensing pixel (60x60 or 1000x1000 m). This project will purchase a scintillometer to measure sensible heat fluxes over distances from 100 to 10,000 m.

Animal Health Component

100%

Research Effort Categories

Basic

(N/A)

Applied

100%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
111	0199	2010	50%
111	0210	2020	50%

Knowledge Area
111 - Conservation and Efficient Use of Water;

Subject Of Investigation
0210 - Water resources; 0199 - Soil and land, general;

Field Of Science
2010 - Physics; 2020 - Engineering;

Keywords

scintigraphy

scintillation counters

heat

heat flow

measurement

heterogeneity

watersheds

water use efficiency

engineering

water resources

equipment

eddies

purchases

remote sensing

Goals / Objectives
We propose to purchase a LAS scintillometer to measure sensible heat fluxes in the Middle Rio Grande Valley of New Mexico over the course of many different studies.

Project Methods
A scintillometer is an instrument that consists of a transmitter and a receiver (Figures 1 - 3). The receiver measures intensity fluctuations in the radiation emitted by the transmitter caused by refractive scattering of turbulent eddies in the scintillometer path. For laser sources, or small aperture scintillometers (SAS), the observed intensity fluctuations are a measure of the structure parameter of the refractive index, Cn2, and the inner scale of turbulence, lo. For large aperture scintillometers (LAS) (Figures 2 and 3), they are a measure of Cn2 only. At optical wavelengths the contribution of temperature fluctuations dominates, i.e., the structure parameter of temperature CT2 can be deduced from the Cn2 measurement. For radio wavelengths (> 1 mm) on the other hand, water vapor fluctuations contribute most to the scintillometer signal, i.e. the structure parameter of moisture Cq2 can be deduced from the Cn2 measurement. Surface fluxes of sensible heat, latent heat and momentum can be determined from scintillometer measurements. Scintillometers can measure sensible and latent heat fluxes at scales of 100 to 5000 m which is similar to the scale of the LandSat TM and MODIS remote sensing images currently available on a routine basis. Used together with the eddy covariance and Bowen ratio systems that are in operation at several riparian and desert locations in the Middle Rio Grande Valley (New Mexico), scintillometer measurements will allow us to better understand the effect of spatial scales on sensible and latent heat fluxes and to improve SEBAL.

Progress 08/01/03 to 07/31/04

Outputs
A major difficulty for the further development of remote sensing methods for evaluation of sensible and latent heat fluxes over heterogeneous riparian and desert vegetation has been the measurement of these fluxes at a scale similar to the spatial resolution of the remote sensing image. While the spatial length scale of remote sensing images covers a range from 30-90 m (LandSat TM) to 250-1100 m (MODIS, AVHRR) direct methods to measure sensible heat fluxes such as eddy covariance and Bowen ratio only provide point measurements at a scale that may be considerably smaller than the estimate obtained from a remote sensing method. Recently, scintillometry has become a mature technique to measure sensible heat fluxes at scales from 100 to 10,000 m in homogeneous as well as heterogeneous landscapes. Therefore, we have purchased a LAS Large Aperture Scintillometer of Kipp & Zonen, Inc. for testing under New Mexico conditions. First, sensible heat fluxes have been measured over a 300 m transect on the campus of New Mexico Tech and a 1000 m transect in the desert of the Sevilleta National Wildlife Refuge near Socorro to become familiar with the instrument. Now, the scintillometer has been installed at the Candelaria Farms near Albuquerque to measure sensible heat fluxes over a 250 m transect in an alfalfa field. The scintillometer has provided us with reliable sensible heat flux measurements at the scale of 100 to 1000 m. Graduate students can operate the scintillometer with little training. However, the selection of measurement transects requires a thorough understanding of boundary layer micrometeorology. Scintillometers require tall stable towers for installation which adds to the costs of scintillometer transects. The positive experience with our first scintillometer has resulted in the purchase of three more scintillometers that will be installed during the summer and fall of 2005. It is expected that the four scintillometers will contribute to the calibration of remote methods for evaluation of sensible and latent heat fluxes over New Mexico.

Impacts
The positive experience with the scintillometer has resulted in the purchase of three more scintillometers. The four scintillometers will lead to better regional estimates of evapotranspiration in irrigated lands, riparian corridors, and surrounding range and desert lands in New Mexico.

Publications

• No publications reported this period