Indonesia, Remote Sensing

The most recent land use land cover of Cimanuk Watershed

By the end of last month, flood was hit Garut City, where located in the center of Cimanuk watershed area. Many believed that flood event this time was due to mismanagement of upper stream area.

To have better understanding, we need to employ space-based image analysis to identify the most recent LULC (Land Use Land Cover) of Cimanuk Watershed.

Based-on Landsat OLI 8 acquired on August 10, 2016. The result are as shown in Figure 1, below

LULC of Garut Year 2016
LULC of Garut Year 2016

I used supervised neural netwok (NN) algorithm to extract the above figure. Based-on my evaluation, supervised NN is better than maximum likelihood or minimum distance algorithms. The class is defined in very smooth visualization.

The man-made structures (red color) are appeared in the upperstream, while agriculture (light green) and industrial forest (dark green) are dominant in this region. No doubt, when huge amount of rainfall drop, there will huge run-off be generated. This run-off will bring huge amount of materials.

Affected locations are highlighted in yellow (Sukakarya, Paminggir, Muarasanding, Pakuwon, Haurpanggung, and Sumantri). As we could see, this location is place when main streams ‘meet each other’. These streams loaded with huge amount of material, not only water but also suspended sediments (i.e., soil, mud, rock, logs, etc)

Multispectral data is very hard to be analyzed for high percentage of cloud cover. Fortunately, we have anothe space-based image of radar data of SENTINEL-1 to assess the same area. Data was acquired on October 4, 2016. The following is the result for man-made structures of upper stream of Cimanuk Watershed.

LULC of Cimanuk Watershed from Sentinel-1 data
LULC of Cimanuk Watershed from Sentinel-1 data

 

Sentinel-1 data enhanced the visualization, and we could confirmed, that there are extensive land use transformation in the upper stream.

The Sentinel-1 data has been calibrated and speckle filtering has been employed. Geometric correction also has been done based-on SRTM 3Sec data.

 

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Urban environment

Learning from river-side management in Japan: Rapid assessment using satellite images

As the previous article in this webpage, the reservation of precious waterside areas along river-side in Tokyo are under good condition (light green color along river side). The improvement and development of minor rivers to protect Tokyo from suffered serious damage from floods due to typhoon strikes are also well prepared and maintained in Japan.

The buffer zone along main river are vary, between 100 to 200 m (see Figure 1). These buffer zones are utilized as open green space for urban inhabitants in dry season. Baseball field, jogging tracks, and small parks are some of the urban green space available here. While in the rainy season or when the runoff relatively higher due to typhoon strikes, the buffer zone along river-side will work to protect the inhabitant from being submerged. River diversion in smaller channel is typical common management in Japan`s urbanized area.

Buffer zones along river-side in Tokyo.  Image acquisition of Landsat 8 OLI was May 2013
Figure 1. Buffer zones along river-side in Tokyo.
Image acquisition of Landsat 7 ETM+ was 4 May 2013. Color composite of bands 754 with image Gram-Schmidt enhancement technique to acquired 15 m resolution.

In contrary, in Great Megapolitan Jakarta, river-side environments are in bad condition. From the rapid assessment  using remotely-sensed image we can see that there is no buffer zone available (see Figure 2). Uncontrolled development can be seen from the density of man-made objects along river-side.

There is no buffer zone
Figure 2. Satellite image of Jakarta.
Image acquisition of Landsat 8 OLI was 25 August 2013. Color composite of bands 754 with image Gram-Schmidt enhancement technique to acquired 15 m resolution.

Furthermore, if we compare the topography condition between two great megapolitan area, we could understand that there is quite similar characteristics between Jakarta and Tokyo as shown in the following figures.

Comparing topography
Comparing topography of Jakarta and Tokyo. We draw line across Jakarta and Tokyo to show the cross-section of topography condition form north to southern part of the cities.
Source: Google Earth, elevation profile fuction

Tokyo`s elevation profile along 64.5 km is lower than Jakarta`s elevation profile, but there was no huge-wide floods event during the last two decades in Tokyo Megapolitan Area since the better management in buffer zone always done regularly.

Water will flow from the higher elevation to lower elevation, we need to manage many variables (including; land use land cover in the upper streams and down streams, physical condition, and  socio-environment condition) in order to overcome the flood. One of the solution of floods in Great Megapolitan Jakarta is management along river-side. It will not be achieved in short-term project, however it could begin now!

Remote Sensing

Monitoring flood in Europe: Optimizing Landsat 8

Flooding in Europe is due to non-stop heavy rainy since the late of May to the beginning of June 2013. In this study we employ NDWI index in order to highlighted water along the river side.

NDWI is Normalized Difference Water Indices. NDWI were computed for each pixel using the equation from Gao, 1996. The equation of NDWI is as follow:

NDWI = (ToA of band 4 – ToA of band 5)/(ToA of band 4+ ToA of band 5)

Algorithm employed in this study:

1. Atm correction (dark object substraction) on DN images

2. DN conversion into ToA (Top of Atmospheric) relfectance

3. NDWI calculation

4. Superimposed “water detected image” on vector map from Yahoo street

5. Employing transparency level on “water detected image”

The study area is Elbe River, part of Elbe drainage basin in Germany. We employ Landsat 8 (path 193/row 23), acquisition date was on June 7, 2013.

Normal river-water situation
Normal river-water situation

It can be seen from the “water detected image” below that small residential along the river side was suffered from the overflow water from the Elbe River.

In the northern part, from Abbendorf to Warnau. While in the northern part to the southern part, from Rabel to Tangermunde are suffered of flood.

Flooding situation along river-side. Water detected is highlighted in light white color. Transparency level is 50%
Flooding situation along river-side. Water detected is highlighted in light white color. Transparency level is 50%