Investigators:

Principal Investigator:
Dr. Shunlin Liang, Assistant Professor
Department of Geography, University of Maryland
2181 LeFrak Hall, College Park, MD 20742
Phone: (301) 405-4556; Fax: (301) 314-9299
Email: sliang@geog.umd.edu

Co-Investigator:
Dr. Charles Walthall, USDA Agricultural Research Service
Phone: (301) 504-6074
Email: cwalthal@asrr.arsusda.gov

Co-Investigator:
Dr. Craig Daughtry, USDA Agricultural Research Service
Phone: (301) 504-5015
Email: cdaughtr@asrr.arsusda.gov
 
 

Objective:

Our primary objective is to validate and quantify the accuracy of MODIS land surface reflectance and albedo products with corresponding MISR parameters, and to validate different formulae for calculating surface reflectance and albedo parameters that can be used as checks for the original EOS algorithms.  We propose to achieve this by:

a)   participating EOS field measurements and augmenting correlative measurements of land surface reflectance/albedo under conditions that have been specified in the PI's validation plans.

b)   validating the methodology of scaling point/plot measurements to MODIS/MISR pixel sizes using high spatial resolution imagery such as low altitude hyperspectral data, ASTER and LANDSAT 7 observations for better quantification of uncertainties over heterogeneous regions.

c)   validating an alternative coupled atmosphere-surface algorithm for retrieving surface reflectance, BRDF and albedo simultaneously, and an alternative algorithm for calculating surface broadband albedos directly from TOA measurements without performing atmospheric correction.  Those independent algorithms can be used for detecting any possible poor performances of existing algorithms under a variety of different conditions that are not represented by test sites.

d)   conducting end-to-end certainty evaluation of MODIS surface reflectance and BRDF/albedo retrieval using retrieved MISR aerosol products and different surface BRDF models for temporally variable cover types.

e)   testing algorithms for calculating new albedo products directly used for ecological and climatic modeling.
 
 

Summer 1998 Field Campaign:
 

TEST SITE:

The study area is approximately 10km by 10km square, centered around the USDA Beltsville Agricultural Research Center (BARC) in Beltsville, Maryland (39 N latitude, 76.85 W longitude).  The location is about 21km northeast of downtown Washington DC, in Suburban Maryland north of the NASA Goddard Space Flight Center (GSFC) just outside of the Washington Capital Beltway. We have both intensive sites (two crop lands, each with about  0.5km by 1km) and the extensive 10km by 10km site which contains a wide variety of land use/land cover types from urban to forest.

  Area Overview Map         Study Area TM Image         Study Area Landuse map

(click to enlarge)

The average annual temperature for this region is 55 F and the average total precipitation is 35 inches.  Winter temperatures range from 45 F (daily maximum) to 28 F (daily minimum) and summer daytime temperatures usually exceed 86 F.  There is no pronounced rainy season, however shower activity increases during summer months.

This portion of Maryland lies just below the fall line at the western edge of the coastal plain.  The area has a rolling topography and averages 22m above sea level.

Soils in the region are primarily Ultisols and Entisols and some limited areas of Alfisols.  These range from fine to coarse loam and are well- to moderately well-drained.  Vegetation consists of a mix of deciduous and evergreen forests made up mainly of Dogwood, Hickory, and American Holly.
 

A BRIEF SUMMARY:

   We conducted our first field campaign on the USDA Agricultural Research Service Beltsville Agricultural Research Center (BARC) in Beltsville, Maryland. A major objective of this experiment was to gain practical experience and assess logistics and instrumentation requirements. A base line data set was obtained that includes some surface measurements, an airborne data set, and a near-coincident SPOT overpass Our targeted time interval was August 18 for a Landsat5 overpass and August 19 for a SPOT4 overpass. It lasted about two weeks.

1. Participants   Groups represented in the field were Shunlin Liang's UMD group, Charlie Walthall and Craig Daughtry's USDA-ARS group, Wolfgang Lucht's BU group (Alan Strahler), Anne Vermeulen's atmospheric correction/aerosols group (Eric Vermote), and Jeff Morisette's MODLAND's validation group. Eric Vermote visited the site before the campaign and Jeff Privette visited the site and examined the CIMEL mounting during the campaign.

2. Tower   We put up a 10m tower in a large homogeneous corn field at BARC that is being used for long-term precision farming research. The tower is equipped with the SW and NIR CM-21 albedometers (top) and a CIMEL (middle). The albedo samples were recorded every 1 minute during the campaign and are set to continuously measure at 10 minutes for long-term continuous observations. The tower CIMEL is for sun photometry and also does a BRDF scan, once every one hour. The tower was designed with a concrete base. To avoid damaging crops, we are using a steel plate as the base.

  Tower and Instrument Installation

(click to enlarge)
 

  A Corner of the Corn Field

(click to enlarge)
 

3. Airborne Data   We used a twin-engined aircraft with a commercial VNIR hyperspectral sensor to acquire data on August 19 when SPOT4 flew over. The weather forecast in the late afternoon of August 17 indicated that the 18th would be very cloudy and we therefore cancelled the flight. We planned two flight altitudes for two spatial resolutions: 1m and 4 m, which were estimated to take approximately 2 hours. Because of the increasing cloudiness on the morning of the 19th, we cancelled the 1m flight. Thus, we acquired wall-to-wall 60band 4m-resolution airborne imagery near coincident with the SPOT overpass under partly cloudy conditions for roughly 80 percent of our 10 km x 10km study area.

4. Albedo and spectral reflectance measurements   We made albedo measurements in the corn field at sites with extreme conditions: very sparse and very dense. We also made measurements along three transects. These sites were measured for LAI mapping. For albedo and BRDF mapping, optimal sampling strategy needs to be further developed. Off the corn field, we made measurements of other (low height) cover types. Particularly interesting, were measurements of albedo diurnal cycles for several vegetation types that were made over several days following the overpass. Two SE590s were used to measure spectral reflectance for different cover types. Reflectance measurements were made at a site and then the instrumentation was loaded into a vehicle and carried to additional sites where the procedures were repeated.
 

Preliminary Monthly Albedo Measurements taken from the Tower

(click to enlarge)
 
 

5. Canopy configuration and leaf optics   We measured corn canopy characteristics around the tower: height of the corn plant, number of leaves, dimensions of leaves and heights of these leaves in the branch, etc. Leaf reflectance and transmittance were measured in the USDA laboratory.

6. LAI and Fpar   We did detailed LAI measurements around the tower and at the sites where albedo measurements took place. Fpar was also measured at limited sites, but not simultaneously with the airborne data.

7. GPS   All sites were flagged and geolocated using a differential GPS with 20cm horizontal accuracy.

8. Other data   The corn field is heavily instrumented with soil moisture sensors. Soil moisture data are transferred to USDA computers via telephone lines. They were not completely operational during our field campaign. Sunphotometers at NASA/Goddard operated during the campaign for aerosol and water vapor. A total of 4-5 weather stations measured solar radiation and other meteorological variables throughout BARC. Different satellite imagery are being or will be collected, including TM, SPOT4, SPOT-VEGETATION, SeaWiFs, AVHRR, ATSR-2, and GOES.
 
 

This project is part of the NASA EOS Validation Program.
 

Last Updated: June 6, 1999