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Spatial Extent: Temperate East Asia -- China, Mongolia, South Korea, North Korea, Japan, Siberia and Far East of Russia.
Spatial Resolution: 1 km
Temporal Characteristics:  

Date Classes Represented:

Snapshot

Time Steps Available:

Snapshot

Dates represented:

March 1, 1999 to November 30, 1999
   

These data were originally developed at the University of New Hampshire by Xiangming Xiao and colleagues. These SPOT VEGETATION-derived data products are being distributed free of charge. Recipients have a responsibility to:

1. Acknowledge the University of New Hampshire, EOS-WEBSTER Earth Science Information Partner (ESIP) as the data distributor when used in subsequent models or publications.

2. Pledge not to use any these data in any product which will be sold.

 

Summary:

The collection contains data sets that describe spatial and temporal variations of land cover of temperate East Asia, using VEGETATION sensor data from the SPOT 4 satellite. Twenty-seven 10-day synthesis products of VEGETATION (VGT S-10) over the period of March 1 to November 30, 1999 were acquired and analyzed. The spatial extent of this data collection covers China, Mongolia, North Korea, South Korea, Japan, Siberia and Far East of Russia. One data set is currently available with two variables; it is envisioned that new data sets will be added in the near future.

These data are provided in the Lambert Azimuthal Equal Area projection with a 1 km cell size.

Currently Available Data Sets:

Table 1

Data Sets

Variables

1) Snow/Ice Cover

a) Normalized Difference Snow and Ice Index (NDSII)

b) Snow/Ice Cover Thematic Image

 

SPOT Image VEGETATION (VGT-S10) Data Product

 

Twenty-seven VGT-S10 data products were acquired for this project between the dates of March 1, 1999 and November 30, 1999. Three standard VGT products are provided to users: VGT-P (physical product), VGT-S1 (daily synthesis) and VGT-S10 (10-day synthesis). In the VGT-S (1,10), the pixels selected for synthesis are based on the selection of the maximum NDVI value to ensure global land coverage with a minimum effect of cloud cover. Each pixel of VGT-S products represents a ground area of approximately 1 km2. For more information about SPOT or SPOT VGT products please refer to the SPOT Image Website listed in the References.

 

For each month there are three 10-day composites (Table 2):

 

Table 2

Composite
Period

Days of the month

1

1-10

2

11-20

3

21-end of month

 

SPOT VGT-S10 products include the following bands (Table 3):

 

Table 3

Band

Band Range (nm)

B0

430 – 470

B2

610 – 680

B3

780 – 890

MIR

1580 – 1750

NDVI

SPOT-calculated NDVI

 

The following SPOT VGT-S10 products were acquired for calculation of the data sets presented in this collection (Table 4):

 

Table 4

SPOT VGT-S10
Composites Acquired

March 1-10, 1999

June 1-10, 1999

 September 1-10, 1999

March 11-20, 1999

 June 11-20, 1999 September 11-20, 1999
March 21-31, 1999 June 21-30, 1999 September 21-30, 1999
April 1-10, 1999 July 1-10, 1999 October 1-10, 1999
April 11-20, 1999 July 11-20, 1999 October 11-20, 1999
April 21-30, 1999 July 21-31, 1999 October 21-31, 1999
May 1-10, 1999 August 1-10, 1999 November 1-10, 1999
May 11-20, 1999 August 11-20, 1999 November 11-20, 1999
May 21-31, 1999 August 21-31, 1999 November 21-30, 1999

 

 

Data Processing of SPOT VGT-S10 Composites

Each 10-day composite (Table 4) contained the four spectral bands in 16-bit Digital Numbers (DN). These DN values were converted to reflectance by using Equation 1 and parameters provided by SPOT Image. The original VGT data were provided in the Lambert Conformal Conic projection. The composites were re-projected to Lambert Azimuthal Equal Area projection at 1-km resolution, using the nearest neighbor re-sampling scheme. The reflectance values of the four spectral bands were then used in data analysis, as described below, to created the data sets in this collection.

 

Equation 1

Reflectance = [0.0005 x DN]

 

Calculation of Normalized Difference Snow/Ice Index (NDSII)

Snow and ice have very high reflectance values in visible spectral bands (blue, green and red), but very low reflectance in mid-infrared band. For VGT data, we proposed the normalized difference snow/ice index (NDSII), using spectral reflectance values of red and mid-infrared bands (Equation 2). NDSII is similar to the normalized difference snow index (NDSI) proposed by Hall et al. (1995,1998), in which spectral reflectance values of green and mid-infrared bands were used. As VGT provides daily images of the globe at 1-km resolution, VGT data offer a new opportunity for mapping and monitoring of snow and ice cover across large spatial scales.

 

Equation 2

NDSII = [(Band 2 – MIR)/(Band 2 + MIR)]

 

A floating point NDSII file (in a range of –1.0 to 1.0) was generated for each 10-day composite. Therefore, 27 NDSII image holdings are available for the NDSII variable in the Snow/Ice Cover data set (Table 1).

 

Generation of thematic maps for snow/Ice cover

A threshold approach is used to generate a thematic map of snow/ice cover for each of the 18 composites (Table 4), using both NDSII values and NIR reflectance (band 3 in VGT). We used the same thresholds proposed by Hall et al. (1995,1998) for NDSI to delineate ice and snow cover, that is, NDSII values greater than 0.40 (Xiao et al., 2000a.b; Hall et al., 1995; 1998). Snow/ice cover was assigned to pixels where the NDSII ³ 0.40 and Band 3 (NIR) > 0.11.

Each of the 18 image files produced from this analysis is byte coverage with pixel values ranging from 1 to 2 and fill values represented by 0 (Table 5).

 

Table 5

Cover Type

Pixel Value

Non-snow/ice

1

Snow/Ice

2

Fill Values
(data out of range)

0

 

 

References:

Hall, D.K., Foster, J.L., Verbyla, D.L., and Klein, A.G. 1998. Assessment of snow-cover mapping accuracy in a variety of vegetation-cover densities in central Alaska. Rem. Sens. Environ. 66: 129-137.

Hall, D.K., Riggs, G.A., and Salomonson, V.V. 1995. Development of methods for mapping global snow cover using moderate resolution imaging spectroradiometer data. Rem. Sens. Environ. 54: 127-140.

SPOT Image. 2000. SPOT Web Site.

Xiao, X., Moore III, B., Qin, X., Shen, Z., and Boles, S. 2000a (in review). Large-scale observation of alpine snow and ice cover in Asia using image data from Vegetation sensor in SPOT 4. Submitted to Int. J. Rem. Sens. January 27, 2000.

Xiao, X., Shen, Z., and Qin, X. 2000b (in press). Assessing the potential of Vegetation sensor data for mapping snow and ice cover: a normalized difference snow and ice index. Submitted to Int. J. Rem. Sens. March 28, 2000.

 

 

Data Provider:

Xiangming Xiao, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, Morse Hall, University of New Hampshire, Durham, New Hampshire, USA. Ph: 603.862.1792, Fax: 603.862.0188, Email: xiangming.xiao@unh.edu.

 

Latest Data Update:

6/30/2000

Last Doc. Updated:

6/27/2000

Doc. Updated By:

Shannon Spencer

 

 

 

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