Spatial Modeling of Mosquito Densities Using MODIS Enhanced Vegetation Index (EVI) and Near

Ground Humidity Indexes: adult female Culex tarsalis and Aedes vexans clustering in Colorado

and Louisiana

A PRESENTATION TO THE SUMMER COLLOQUIUM ON CLIMATE AND HEALTHJULY 23, 2004, NCAR, BOULDER COLORADO

RUSSELL BARBOUR PH.D.

VECTOR ECOLOGY LABORATORY

YALE SCHOOL OF MEDICINE

NEW HAVEN CT.

MODELING VERSUS INTERPOLATION

• LINEAR MODELING ATTEMPTS TO IDENTIFY FACTORS THAT INFLUENCE THE PARAMETERS OF INTEREST AND EXPLAIN OBSERVED VARIATION

• SPATIAL MODELING OR INTERPOLATION USE THE MATHEMATICAL PROPERTIES OF THE DATA ITSELF TO ESTIMATE VALUES AT UNKNOWN LOCATIONS

LECTURE OUTLINE

• Review basic concepts of spatial auto-correlation

• Demonstrate application of these methods to estimate mosquito vectors of West Nile Virus

BASIC CONCEPTS OF SPATIAL AUTO-CORRELATION

Tobler’s first law of geography:Everything is related to everything else, but near things

are more related than distant things

Auto- Correlation violates the assumption of independence in that is made in most statistical tests

Ordinary Least Squares Regression (OLS) for example, will tend to Type I Error ( falsely find significant relationships) if auto-correlation is present

Auto-Correlation can be used to estimate values at un-sampled locations

QUANTIFYING AUTO-CORRELATION

Moran’s I

Geary’s C ratio

Anselin’s Local Index of Spatial Autocorrelation (LISA) 0R Local Moran’s I

Moran’s I

• Similar to Pearson’s correlation coefficient, values between –1.0 and + 1.

• Index for dispersion/random/cluster patterns– Indices close to zero, indicate random pattern– Indices above zero indicate a tendency toward

clustering– Indices below zero indicate a tendency toward

dispersion/uniform– Most commonly reported indicator of spatial auto-

correlation• Differences from correlation coefficient are:

– one variable only, not two variables– Incorporates weights (wij) which index “distance”

between the locations

MORAN’S I CONTINUED

• GLOBAL MORANS’ IEstimates the level of aggregation of values or clustering in space for

all observations

• Correlogram Morans’I calculated for observations grouped into specific distances

TYPES OF SPATIAL STRUCTUREDETECTED BY POSITIVE MORANS’I

VALUES

• CLUSTERS:DATA FOUND IN CLOSE PROXIMITY

• TRENDS:A GRADIENT USUALLY CAUSED BY A GEOGRAPHIC FEATURE (NON-

STATIONARITY)• AUTO-CORRELATION:

SIMILARITY OF OBSERVATIONS CLOSE TO EACH OTHER. A CLUSTER MAY OR MAY NOT HAVE AUTO- CORRELATION

STATIONARITY IN SPACE

• FIRST ORDER (STRICT) STATIONARITY

A property of a spatial process where all of the spatial random variables have the same mean and variance value.

• INTRINSIC (WEAK) STATIONARITY

An assumption that the data comes from a random process with a constant mean, and a semivariogram that only depends on the distance and direction separating any two locations.

SOURCE : U. OF ARIZONA

PURPOSE OF LOUISIANA SPATIAL MOSQUITO ESTIMATES

• INDICATE AREAS OF HUMAN RISK OF WEST NILE VIRUS

• ASSIST DECISION MAKERS FOR VECTOR CONTROL INTERVENTIONS

• ASSESS THE EFFECTIVENESS OF CONTROL MEASURES

• ESTIMATES HAVE NO EXPLANATORY VALUE, STRICTLY A PROCESS OF CAPTURING MATHEMATICAL RELATIONSHIPS

Aedes vexans

• FLOOD WATER MOSQUITO

• STRONG FLIER > 24 Km/ DAY

• AGGRESSIVE HUMAN BITER

• LOW INFECTION RATES

• HIGH TRANSMISSION EFFICIENCY IF SYSTEMICALLY INFECTED (TURELL 2001)

SOURCE : SERVICE 1976

Aedes vexans NJ Light Trap Catches 2003 St Tammany

MONTH NUMBER % OF TOTAL

JUNE 30312 65.01%

MAY 8144 24.69%

MARCH 1565 24.69%

APRIL 6243 21.52%

Spatial Autocorrelation for Point Data:---------------------------------------  Sample size 53  Moran's "I" 0.090325 Spatially random (expected) "I" -0.019231 Standard deviation of "I" 0.040462 Normality significance (Z) 2.707580 = P < .05 Randomization significance (Z) 2.952694 = P < .05 

GLOBAL MORANS’ I Aedes vexans

NJ LIGHT TRAP CATCHES JUNE 2003 ST. TAMMANY PARISH LA

GLOBAL MORANS I VALUES Aedes vexans Catches

NJ Light Traps 2003

MONTH OBS I EXP I P

FEB -0.02 -.019 0.9656

MARCH 0.037 -0.019 0.1402

APRIL 0.081 -0.019 0.0087

MAY 0.167 -0.019 .0000

JUNE 0.090 -0.019 0.0031

CORRELOGRAM FOR JUNE NJ LIGHT TRAP CATCHES ALL SPECIES APRIL 2003

ST TAMMANY PARISH LA.

meters

RANGE

ISOTROPIC VARIOGRAM Aedes vexans APRIL 2003

SAMPLE VARIANCE

MODIS ATMOSPHERE PRODUCTS

• 1-KM SPATIAL RESOLUTION

• USING THE NEAR-INFRARED ALGORITHM DURING THE DAY, 1-KM PIXEL RESOLUTION

• THE SOLAR RETRIEVAL ALGORITHM RELIES ON OBSERVATIONS OF WATER-VAPOR ATTENUATION OF REFLECTED SOLAR RADIATION IN THE NEAR-INFRARED IN THE ATMOSPHERE CLOSE TO THE GROUND

• VALUES REPRESENT THE AMOUNT OF WATER PER PIXEL THAT COULD THEORETICALLY BE PRECIPITATED OUT OF THE ATMOSPHERE

MODIS ATMOSPHERE PRODUCT RELATIONSHIP TO Aedes vexans

• WATER COLUMN PRODUCTS BY NIR AND IR ARE APPROXIMATIONS OF ABSOLUTE HUMIDITY AND SATURATION DEFICIT IN THE LOWER ATMOSPHERE

• THE IR DATA IS PRODUCED FOR BOTH DAY AND NIGHT.. INCLUDES DUSK AND DAWN ESTIMATES

• IS AVAILABLE ON A DAILY BASES

MEASUREMENT OF Aedes vexans MICRO-CLIMATE DISPERSAL PARAMETERS

HATCHING >EMERGENCE > DISPERSAL

RAINFALL STANDING WATER HIGH ABSOLUTE HUMIDITY

CLUSTERING NEAR HOSTSLIGHT TRAP DATAAND VARIOGRAPHY

MORANS’I

MODIS WATER VAPOR PRODUCTS

Aedes vexans Monthly Catches NJ Light Traps VersusMODIS WATER COLUMN IR METHOD VALUES

(DAY + NIGHT ) FEB- JUNE 2003

-5000

0

5000

10000

15000

20000

25000

30000

35000

1 1.5 2 2.5 3 3.5

MODIS WATER VAPOR VALUES

MO

SQ

UIT

O N

UM

BE

RS Y

Predicted Y

Series3

Linear (Predicted Y)

MONTHLY Aedes vexans NJ LIGHT TRAP CATCH NUMBERS VERSUS RAINFALL

-10000

-5000

0

5000

10000

15000

20000

25000

30000

35000

0 2 4 6 8 10 12 14 16 18 20

RAINFALL IN INCHES

Ae

de

s v

ex

an

s n

um

be

rs

Y

Predicted Y

Linear (Predicted Y)

0

1

2

3

0 2 4 6 8

Y

Y

Predicted Y

RAINFALL ON Ae. vexans CLUSTERINGP VALUE .54

-0.4-0.2

00.20.40.60.8

1

0 1 2 3

Y

Y

Predicted Y

CLUSTERING ON MODIS VALUESP VALUE .104

SPATIAL FACTORS ASSOCIATED WITH Aedes vexans DENSITY IN

St TAMMANY PARISH

• MODIS WATER VAPOR PRODUCT .38

• URBAN PRESENCE (POPULATION AND LIGHT) .34

TEMPERATURES ABOVE 90 F

MODIS INFRARED WATER VAPOR COLUMN MONTHLY DATA 2003

MONTH MOSQUITO # MODIS Monthly Product

1 22 1.41

2 5 1.48

3 1565 1.52

4 6243 1.79

5 8144 2.57

6 30312 3.39

7 1322 3.93

8 494 4.01

9 315 3.14

10 1662 2.64

11 1084 2.37

12 97 1.64

Aedes vexans CATCHES in NJ LIGHT TRAPS VERSUS MODIS HUMIDITY MEASURES 2003

START OF HIGH TEMPERATURE

LAKE PONCHATRAIN

ESTIMATED DENSITY OF Aedes vexans ADULTS BY CO-KRIGING LIGHT TRAP AND MODIS HUMIDITY DATA

LIGHT TRAP DATA WITH WEAKER SPATIAL STRUCTURE

• Culex tarsalis IS INCRIMINATED IN THE TRANSMISSION OF WEST NILE VIRUS TO HUMANS IN THE FORT COLLINS COLORADO AREA (NASCI ET AL 2003)

• BREEDS IN ANY SOURCE OF FRESH WATER OTHER THAN TREE HOLES . MULTIPLE GENERATIONS

• IRRIGATION DITCHES HIGHLY FAVORABLE BREEDING AREAS

• FEEDS ON BIRDS THEN SHIFTS TO MAMMALS AND HUMANS AS ABUNDANCE INCREASES

Culex tarsalis

Culex tarsalis DISPERSALFrom (Reisen 2002)

• SLOW MOVING, 1 Km/ DAY

• WIND DRIVEN

• ACTIVITY RELATED TO VEGETATION COVER

Culex tarsalis Clustering near Ft Collins Col. July 2003

Spatial Autocorrelation for Point Data:---------------------------------------  Sample size 70 Moran's "I" -0.010883 Spatially random (expected) “I” -0.014493 Standard deviation of "I“ 0.020686 Normality significance (Z) 0.174495 =p> .10 Randomization significance (Z) 0.179128 =p> .10 

• MODIS REMOTELY SENSED VEGETATION INDEX = ENHANCED VEGETATION INDEX (EVI)

• MODIS WATER VAPOR COLUMN IR DATA

SPATIAL RELATIONSHIPS OF C. tarsalis LIGHT TRAP DATA AND REMOTELY

SENSED MICROCLIMATE INDICATORS

INDICATORS SPATIAL RELATIONSHIP

PRESENCE OF IRRIGATED FARM LAND

.26

EVI .12

WATER VAPOR DATA .34

APPLICATION OF ARTIFICIAL NEURAL NETWORKING (ANN) TO IMPROVE

ESTIMATES

IRRIGATION, VEGETATION AND WATER VAPOR INDICATORS COMBINED BY ARTIFICIAL NEURAL NETWORKING (ANN)

RESPONSE SURFACE

ANN RESPONSE SURFACE = .61 SPATIAL RELATIONSHIP WITH C. tarsalis LIGHT TRAP CATCHES

MODIS ENHANCED VEGETATION INDEX (EVI)2003

JUNE 10

MAY 9

JULY 2

CLUSTERING OF C. tarsalis in RELATIONSHIP TO MODIS EVI VALUES

SPATIAL ASSOCIATION WITH EVI VALUES OF 4000- 6000 DURING MOST OF THE 2003 SEASON

RESULTS

• AN ASSOCIATION APPEARS TO EXIST BETWEEN C. tarsalis AND MODIS EVI AND WATER VAPOR VALUES AT THE COLORADO SITE

• A STRONGER ASSOCIATION BETWEEN Aedes vexans AND MODIS HUMIDITY DATA WAS FOUND AT THE LOUISIANA SITE

• EVEN WEAKLY CLUSTERING SPECIES CAN BE ESTIMATED THROUGH APPLICATION OF SPATIAL STATISTICS AND ARTIFICIAL NEURAL NETWORKS

• MORE ROBUST INTERPRETATION OF LIGHT TRAP DATA IS POSSIBLE

• DAILY MODIS ATMOSPHERIC DATA AVAILABILITY WILL ALLOW FORWARD LOOKING MODELS IN THE NEAR FUTURE