Tuesday, December 17, 2013

Mahmud Hasan Ghani's Internship, Fall 2013 - Part 7

SST Satellite Products 

I mentioned in my last blog that I have found a good correlation in the Aqua MODIS global sea surface temperature (SST) products with our SailBuoy data. Today, I intend to discuss more details about the satellite-derived SST products and how the product is more validated with the reference data.

From several SST products of different resolution of Aqua MODIS, I am using one of the standard products for my comparison. This Aqua MODIS Level 3 global product is a daily global 4 km SST product available on the OceanColor website on a daily basis. Here question may arise, that one full analysis is remained for Terra MODIS which has the same quality SST products. At the beginning stage, I studied both Aqua and Terra MODIS products for the same in situ data. After several comparisons between Aqua MODIS and Terra MODIS, I had decided to go for the Aqua MODIS, as it seemed better relevancy in retrieved data. But that does not neglect the Terra MODIS, when in this term I am focusing one product only. There might be another complete series of analysis which can be interesting to find out the best validated product. Usually, it will take more time to download the images and to process the data to fit with the SailBuoy data. So, there is a scope to more analysis in between the satellite products.
Figure 1: Day-wise SailBuoy SST vs satellite-derived SST.
However, coming to the current analysis, the figure is showing the day-wise surface temperature variation in the Northern Gulf of Mexico from where the SailBuoy started to transmit data on March 15, 2013, and ended on May 15, 2013. I have mentioned that this satellite product is from level 3 products, but there is another option for a day-wise level 2 product on the OceanColor website. It is important to mention this level 2 product, as there is some limitation in the coverage area of the satellite image, which could miss some study area in a particular day. The images are not in similar style for all days to cover the whole Gulf of Mexico; so level 3 global products are better than level 2 to find out the location wise SST values mentioning the latitude and longitude through the daily images. It reduces the chance of missing the right locations and retrieval of SST values.
Figure 2: Scatter plot of satellite-derived SST vs SailBuoy SST (62 days).

Posted By:
Mahmud Hasan Ghani, Norwegian Meteorological Institute

Monday, December 9, 2013

Mahmud Hasan Ghani's Internship, Fall 2013 - Part 6

Trip to Hallingskeid

During this busy and short semester, I passed a good day in Hallinskeid, Norway, on November 18-19. The program was organized by Dr. Lars Hole in a mountain cabin of Hallingskeid, where we were introduced to the traditional Norwegian mountain hiking culture in snowing conditions and had an informal scientific seminar. The seminar was the main objective of this short trip, but we also experienced the Norwegian cabin life in a silent mountain area and had a relaxing break from the packed city life. Hallingskeid is a railway station between Oslo and Bergen inside a snow tunnel; many mountaineers go there for hiking during weekends and stay at the nearest cabins from the station, which are at the slope of the mountain. The station is located at 1,110 meters (3,640 ft) above mean sea level.

 It was a great a time with two other visiting scientists from Cuba and one student from Faroe Island. For all of us, it was a new experience by passing a night in a mountain cabin when the outside temperature was - 8° C and all the horizon was covered with snow. Our cabin was only a few hundred meters away from the nearest station, but, somehow, the most challenging task was to pass this short distance over fresh snow. As we were at the beginning of the snow season this winter, the snow was not compact enough to move freely. At late evening, we had fun over the snow-covered slope of the mountain with sliding and skiing. Dr. Lars is an experienced guy in these conditions; he helped us by providing all kinds of information and materials for the movement at the typical rough weather conditions of Norway.  
Location of Hallingskeid (red dot on map) in relation to Bergen (white dot on map).
Above and below: A few moments at Hallingskeid (photos courtesy of Dr. Lars Hole).

The next morning, there was a scientific session for all of us to present our ongoing research work. I made a PowerPoint presentation to discuss the SailBuoy project and data analysis that I am doing under Deep-C. These days, I am getting interesting comparison results in terms of remote sensing data from Aqua MODIS sea surface salinity (SSS) products, which I have used to compare in the below analysis. Somehow, this satellite date figure is showing the same tracking location against the SailBuoy SSS data, but the data values retrieved from satellite images are giving constant same values for a single day without significant variation. As suggested by Dr. Nico Wienders from Florida State University, I should try new products as usually this SSS product is not as good as it should be. I will try for SMOS, Aquarius, or some other new source of remote sensing data products in the upcoming days to find out the close salinity values for in situ data. In the case of sea surface temperatures, there is good correlation between the two data sets, and results show more validation of the Aqua MODIS products, which I am going to discuss in my next blog.  
Sea surface salinity mapping: Satellite vs. SailBuoy data.

Posted By:
Mahmud Hasan Ghani, Norwegian Meteorological Institute