Rene's World: NDVI: Normalised Difference Vegetation Index a.k.a Vegetation From Space

Exercise 1

1. Describe the two NDVI images.

The first image, which is the image taken from SPOT satellite shows vegetation in January 2000 while the second image is taken from SPOT satellite in August 2000. Addition two images are the precipitation map in Latin America, taken in January and August 2000. Based on the first map given, it shows only a small part of dark green area observed, which is located on the North side of the map. The second map shows a larger area with dark green, which is located in the middle of the map. Dark green region shown in both maps indicate that the vegetation in that region is very healthy. With comparison of both maps, it shows that vegetation is very healthy during August instead of January.

With the reference to the addition two images, which are the precipitation maps, it is observed that there are more precipitation in the middle of the continent during August compared to January. This further explains the reason why vegetation is found to be healthier is the region where there are abundant of precipitation during August compared to January.

2. Where do you find the most abundant vegetation?

Most abundant vegetation can be found in dark green region shown in the map, which is Peru, Bolivia and Brazil during August, where there are abundant of precipitation.

3. Where do you find the least abundant vegetation?

In the region of Chile and Argentina, where precipitation in that region is in a range of 20-50mm/quarter.

4. Compare the precipitation maps for the two seasons and try to explain the changes in vegetation from January to August.

Based on the precipitation map for December to February, it is observed that there is abundant of precipitation on the North of Latin America, as the wind direction is shown to be blowing towards North. Meanwhile, according to the precipitation map for June to August, it shows that there is abundant of precipitation in the middle region of Latin America. Changes in vegetation from January to August is seen by the changes of the health of vegetation. Dark green region in the map indicates that the vegetation is very healthy. Thus, to explain the changes, precipitation brings healthy vegetation. This is due to the basic need of vegetation, water. Abundant amount of precipitation and sunlight helps in the growth of vegetation.

5. Find some areas where there is much variation in the NDVI. By comparing the NDVI with the precipitation maps can you explain the variations?

Brazil and Argentina. In Brazil, it shows a high value of NDVI, while in the Southern part of Argentina, it shows a very low value of NDVI. Both values of NDVI is indicated by dark green and baige colour respectively. The darker the colour, the healthier is the vegetation, and vice versa. Comparing the the precipitation maps, Brazil shows a high precipitation compared to the Southern part of Argentina, which precipitation received is minimum. This variations happened due to the meeting of the needs of vegetation. NDVI shows the health condition of vegetation by obtaining the colour of leaves of vegetation. Green leaves shows healthy vegetation, while baige or light yellow shows unhealthy vegetation. In order for healthy vegetation, water is one of the basic needs. Thus, in Brazil, it receives the maximum precipitation during June to August, which leads to the healthy vegetation conditions. Compared to Southern of Argentina which receives minimum precipitation, vegetation there is very poor.

6. Find some desert areas. Can you explain why precipitation is so low in these areas?

Nothern Peru, Western Boliva, Northern Chile and Southwestern Argentina.

Precipitation is so low in these areas throughout the year is due to the wind patterns. These areas experience changes of wind direction as monsoon season changes throughout the year. Wind in these areas is warmer and drier. The dry air blows through desert regions, which absorbs the moisture and reduce the likelihood of cloud formation and rainfall. High temperatures causes rapid evaporation to take place. Besides, a landscape consisting of mountains around stops moist air from approaching, which then decrease the precipitation.

7. There are some areas with high NDVI values in both seasons. Can you explain why?

Guyana and Paraguay shows high NDVI values in both seasons. This may due to the topography of the area. Both areas are located in low areas, and are not surrounded by any mountains or highlands. Therefore, monsoon which brings rainfall, coming in both ways in different seasons is not blocked by mountains or highlands. Thus, both areas receives sufficient precipitation required for vegetation growth. Thus, both areas have high NDVI values which indicates healthy vegetation.

Exercise 2

8. Observe and describe the variation in the NDVI value during the year 2000.

NDVI value variate from January to December in the year 2000 significantly. From the map given, it is observed that during January, there is only a small region of dark green. Dark green indicates the area where vegetation grows healthily, while blue shows the most healthy vegetation. In the month of February, it is observed that there is a small region with blue spots. This shows a high value of NDVI. Meanwhile, in the month of March to May, we can see that NDVI value increases as the blue region shows an increase in size. In the month of June and July, the blue region spotted increases rapidly, which indicates that the value of NDVI increases too. However, in the month of August, it shows a slow decrease of blue region or dark green, and continue to decrease rapidly in the month of September and in the month of October, it shows no sign of blue or dark green spot. This shows that the value of NDVI increases as blue region increases in size and decreases as blue region or dark green decreases. In the month of October, it shows a very low value of NDVI. In November, NDVI value increases slowly as the darkness of green colour increases in several regions. During December, NDVI value increases as blue region is spotted in the map.

9. In what months is the NDVI at its maximum in the Amazon basin? Can you explain why?

NDVI shows its maximum value in the Amazon basin in the month of July. NDVI value shows the health of vegetation on Earth surface. The higher the value of NDVI, the healthier is the vegetation. Blue colour in the map shows the highest value of NDVI. Based on the precipitation map provided, this is because during June, July and August, there is abundant of precipitation observed. As water is one of the basic needs of vegetation growth, vegetation shows its maximum health during these three months.

10. Observe the December image for the northeastern part of Brazil along the Atlantic coast and inland. Can you explain the vegetation pattern?

The vegetation in the northeastern part of Brazil along the Atlantic coast and inland shows a moderate health. The light green shown in December image indicates that vegetation there is not in an excellent condition. As it goes along the Atlantic coast and inland, until it almost reaches the Eastern part of Brazil, it shows a lighter green compared to the upper part. This shows a lower health condition of vegetation. This may due to the low precipitation of the Eastern part of Brazil.

11. Can you explain the variation in vegetation along the Pacific coast?

Pacific coast have a very low variation in vegetation. This is shown through the baige colour in the map. Along the Pacific coast, it is observed that it is almost desert area, which only have maximum precipitation of 20-50mm/quarter every month. This leads to unsuitable condition for the growth of vegetation, as vegetation requires precipitation for growth. Thus, almost zero vegetation is observed throughout the year.

12. Compare the information on climate as described in the maps in a normal school atlas with the NDVI images. How are the yearly changes of the location of the Inter-Tropical Convergence Zone (ITCZ) reflected in the NDVI images?

Information on climate as described in the maps in a normal school atlas is just the basic information. It shows how climate variate, however, it does not have detailed information as NDVI images do. NDVI images are able to show the region with the maximum or minimum precipitation. In addition, an animation can be played in order to see the variation of climate at once, without needing to have many images on hand at once. Besides, normal school atlas climate information is hard copy, while NDVI is digitised information. This enables user to manipulate the data with applications in order to get the information that he desired.

Inter-tropical convergence Zone (ITCZ) is the area encircling the Earth near the equator, where the northeast and southeast trade winds come together. It is also known as the monsoon trough, when it is drawn into and merges with a monsoonal circulation. ITCZ is formed by vertical motion largely appearing as convective activity of thunderstorms driven by solar heating, which effectively draw air in, which is also known as trade winds. The rising air produces high cloudiness, frequent thunderstorms, and heavy rainfall within the zone. ITCZ changes north and south seasonly with the Sun. As ITCZ changes its location yearly, it is reflected in NDVI images. The growth and health of vegetation is the direct reflection of ITCZ’s effect. ITCZ causes a part of the continent to be extremely dry, while the other part of the continent to be very wet, with thunderstorms. Regions which are extremely dry will have poor vegetation, which is indicated in NDVI images with light green or baige colour of the map. Meanwhile, in regions with wet weather, vegetation shows a healthy condition, which is indicated as dark green in NDVI images.