A Comparison Study Between
Ground- Truth Temperature Data of
Mitchell Lake and the Temperature
Data Obtained Using MODIS
Satellite Images.
Amber Patrick
Erin Manitou
Department of Earth and Environmental Sciences
The University of Texas at San Antonio
EES 5053, Remote Sensing
Fall, 2006
Outline
Objectives
Background Information
Mitchell Lake
MODIS data
Ground Truth Data
Methods
Results
Conclusion
Objectives
To assess whether or not MODIS
images are a quality indicator of lake
temperature
To compare the remotely sensed data
with ground-truth data for comparison
Mitchell Lake
Cibolo Creek
San Geronimo
Upper Salado Creek
Upper Leon Creek
Culebra Creek
Martinez Creek
Upper San Antonio RiverLower Salado Creek
Medio Creek
Cibolo Creek
Medina River
Lower Leon Creek
Calaveras Creek
Lower San Antonio River
Atascosa River
Elm Creek
Atascosa River
Bexar county map showing
watershed and Mitchell Lake.
Major Highway systems are also
shown.
Coordinate System: NAD 1983
State Plane Texas South Central
FIPS 4204 Feet
Mitchell Lake Background
Information
Mitchell Lake Logistics
Located SW of city of San Antonio
Coordinates: 29º32’N Latitude and
-98º28’W Longitude.
Average lake depth is less than 8 feet
600 acres body of water centered on
1,300 acres of wetlands
One of the two natural lake in state of
Texas
Mitchell Lake Background
Information
Mitchell Lake as Sludge Lagoon
Lake was damned in early 1900’s and
received raw sewage from the city of San
Antonio area until 1930’s
Obviously, poor water quality resulted with
problems such as odorous algal blooms and
sever eutrophication of the lake
From 1987 until present time, the lake is
receiving only treated water from the Leon
Valley Water Treatment Facility
Mitchell Lake Background
Information
Mitchell Lake as Wildlife Refuge
Acts as a bird sanctuary for over 300 species of
migratory birds that pass through the area each year
Lake is owned by SAWS, but is overseen by National
Audubon Society
MODIS Background
Information
MODIS (Moderate-resolution Imaging Spectroradiometer) was
launched on board the Terra satellite (sun-synchronous) in 1999
Terra orbit is north to south so that it crosses the equator in the
morning.
Terra passes over Mitchell lake at approx. 1:30 am and 1:30pm
Acquires data in 36 spectral bands ranging in wavelengths from
0.4μm to 14.4μm
Swath dimensions are 2,300km x 10km
Spatial resolution of 250m (bands 1-2), 500m (bands 3-7), 1000m
(bands 8-36)
Radiometric sensitivity of 12 bits
Ground-Truth Data
Data acquisition began August 21, 2006
Data acquired by Dr. Murray,
Dr.Bodour and Magdalis Morales
(undergraduate student)
Data acquired using a Troll 9000Pro XP
probe
The probe is located on the south rim of
Basin #5 approximately 5 feet under the
surface.
Location of Probe
*
Methods
Images obtained from
the EOS gateway
website
We used the MODIS
reproject tool to convert
the downloaded files to
.tif files for use in ENVI
In ENVI, we used band
math equation to
convert pixel value to
degrees K
Methods Continued….
Density slice was
applied to each
image with 25
different temperate
ranges from 286 K to
332 K
New color every 3
degrees K
Methods
ROI
An ROI was made
of Mitchell Lake and
applied to each
image
Temperatures
compared with
ground-truth data
Results
Temperature data for Day 228 (8-16-06) per
pixel
115
105
Temp
95
(degrees F)
85
75
Day
Night
1 2 3 4 5 6 7 8 9
Pixel Number
Results…
Temp data for Pixel #4
110
100
Temp (F)
90
80
70
222 223 225 228 229 230 232 237 239
Julian dates
Day temp
Night temp
Conclusions
Lack of consistent data proved to be a
problem in accurately comparing remotely
sensed products with ground-truth data
Ground truth data not compatible with
remotely sensed data due to different location
of probe
MODIS doesn’t seem to be useful for gaining
accurate temperature data for a water body as
small as Mitchell Lake.
Factors Affecting Project Results
Cloud covering area of interest. (We were not
able to use Aqua data as originally planned
due to excessive cloud cover.)
Probe location too deep for accurate
comparisons to be made.
MODIS images has too big of a spatial
resolution for such a small subject area.
Landsat 7 has a better spatial resolution(15m).
Images from other more appropriate sensors
are costly, MODIS images are free from the
EOS Gateway.
References
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