Global environmental data for mapping infectious disease distribution

Abstract

This contribution documents the satellite data archives, data processing methods and temporal Fourier analysis (TFA) techniques used to create the remotely sensed datasets on the DVD distributed with this volume. The aim is to provide a detailed reference guide to the genesis of the data, rather than a standard review. These remotely sensed data cover the entire globe at either 1 x 1 or 8 x 8 km spatial resolution. We briefly evaluate the relationships between the 1 x 1 and 8 x 8 km global TFA products to explore their inter-compatibility. The 8 x 8 km TFA surfaces are used in the mapping procedures detailed in the subsequent disease mapping reviews, since the 1 x 1 km products have been validated less widely. Details are also provided on additional, current and planned sensors that should be able to provide continuity with these environmental variable surfaces, as well as other sources of global data that may be used for mapping infectious disease.

Figure 1

a–n Panel of the fourteen 8 × 8 km NOAA-AVHRR NDVI TFA images (a) a0, mean, (b) mn, minimum and (c) mx, maximum signal recomposed from the first three Fourier cycles. The amplitude of the (d) a1, annual cycle, (e) a2, bi-annual and (f) a3, tri-annual are also shown, in addition to the (g) p1, phase of annual, (h) p2, bi-annual, (i) and p3, tri-annual cycle in months. The proportion of the variance in the original time series described by the (j) d1, the annual, (k) d2, the bi-annual, (l) d3, the tri-annual and (m) da, all three cycles combined is also shown with (n) vr, the variance of the original data time series. Data are histogram equalized stretched from the minimum data value (black, also water mask) to maximum (white) for display.

Figure 2

a,b The lower reaches of the Nile river in Egypt illustrate the difference between the 8 × 8 km spatial resolution imagery (on the left) and the 1 × 1 km imagery (right). Images are of the mean NOAA-AVHRR NDVI TFA a0 product (Table 3). Data are histogram equalized stretched from the minimum data value (black, also water mask) to maximum (white) for display.

Figure 3

Latitudinal sample regions, (a) 90–70°N, (b) 70–50°N, (c) 50–30°N, (d) 30–10°N, (e) 10N–10°S, (f) 10–30°S, (g) 30–50°S, (h) 50–90°S.

Figure 4

a–f Scatterplots for latitudinal segments shown in Figure 3 of 8 × 8 km imagery sample points against 1 × 1 km imagery sample points for 50°N–30°N for MIR (a), LST (b) and NDVI (c) and for 10°N–10°S for MIR (d), LST (e) and NDVI (f). One-to-one lines (dashed) are added for ease of interpretation. Solid lines (and equations) are least squares linear fits to the data.