Record Details

Bathymetry Points, Lake Victoria, vector points, 1900 - 2017, V7

Harvard Dataverse (Africa Rice Center, Bioversity International, CCAFS, CIAT, IFPRI, IRRI and WorldFish)

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Title Bathymetry Points, Lake Victoria, vector points, 1900 - 2017, V7
 
Identifier https://doi.org/10.7910/DVN/75JI3A
 
Creator Hamilton, Stuart
Kayanda, Robert
Ongore, Collins
Krach, Noah
 
Publisher Harvard Dataverse
 
Description Bathymetry Points, Lake Victoria, vector point, 1900-2017




Reference Information and Units:



Projected Coordinate System: Africa Lambert Conformal Conic


ESRI:102024 (https://epsg.io/102024)


GCS: GCS_WGS_1984






File Naming Convention:


LV_Bathymetry_Points_V7.shp





Data Origin:


Admiral Bathymetric Maps:


Description: British admiral bathymetry maps of the lake. Maps were scanned and georeferenced. Once georeferenced the depth points were digitized


Points: Approximately 5,212


Year: 1900-1955




Depth Sounder:


Description: Depth readings taken from a depth sounder were read into ArcMap using X, Y coordinates


Points: Approximately 5,888


Year: 2013




German Bathymetry Map:


Description: A German bathymetry map was scanned and georeferenced. Once georeferenced the depth points were digitized.


Points: Approximately 50


Year: 1913




Acoustic Surveys from Nafirri:


Description: Instruments used are two Depth Profiling systems (a submersible Conductivity Temperature-Depth profiling system (CTD, Sea and Sun Technologies)
and a YSI 650 multiparameter Sonde). Readings were read into ArcMap using X, Y coordinates.


Date: 11/2015:


Approximately 55 points


Date: 8/2016


Approximately 50 points




Limnology Survey from Nafirri:


Description: Limnology survey using acoustic equipment and GPS


Points: Approximately 10


Date: 2007/2008





Sounding Data:


Description: Depth readings taken from a depth sounder were read into ArcMap using X, Y coordinates


Points: Approximately 17,200


Date: 2009




Acoustic Sounder Strata Data:


Description: Points were taken to determine the strata of the lake by using a Simrad EK60 echo sounder.
These points contained Z values. The points were read into ArcMap using X, Y coordinates


Points: Approximately 45


Date: 2009




Lake Victoria Bathymetric Survey For EAC/LVBC:


Description: Points were taken using a single beam echo sounder 200kHz and were provided from Ola at MMT. These points are concentrated in three bays, Mwanza Gulf (TZ), Kisumu (KY), and Port Bell (UG).


Points: Approximately 120,000


Date: 2007




Lake Victoria Regional Hydro-acoustics Working Group:


Description: The survey was conducted by the Lake Victoria Regional Hydroacoustics Working Group under coordination of LVFO with NSF project funds. It was conducted using Tanzania's RV. Lake Victoria Explorer.


Points: Approximately 3,945,260


Date: 09/12/2017 – 10/5/2017






Data Development:


The final bathymetry points were created by converting all sources to the same unit(meters). Once all sources were in the same unit they were combined into the same file. When all points were in the same file a spatial query was ran to select all the bathymetry points that fell outside of the Lake Victoria shoreline polygon. Any point that was located outside of the shoreline polygon was removed from the file. The next step was to remove the redundant points. PostgresSQL was used to find all the points that were within 100 meters from another point (SQL Code 1). One of the points would be removed from the final set of points to clean up the data. The points that were obtained from the survey conducted for the EAC/LVBC were not included in the removing of points within 100 meters of one another. Any point from version 6 that was located within 100 meters of a point from the Lake Victoria Regional Hydro-acoustics Working Group dataset, was removed. All points from the acoustic survey conducted by Lake Victoria Regional Hydro-acoustics Working Group were kept regardless of their distance from each other. PostgresSQL was also used to check the depths of points in relation to points around them to determine outliers (SQL Code 2). Outliers were double checked and removed if not deemed plausible. Points that were denoted as “greater than” the recorded depth were removed if the depth was less than 60.96 meters.




SQL Code 1: Finds all points within 100 meters of another point




select a.objectid, b.objectid


from lv_bathymetry_points_v5 as a, lv_bathymetry_points_v5 as b


where st_distance(a.geom,b.geom) < 100


and a.objectid != b.objectid




SQL Code 2: Checks for points with depths that are outliers compared to neighbor points




select a.objectid, b.objectid, (@(a.z - b.z)) as z_diff


from lv_bathymetry_points_v5 as a, lv_bathymetry_points_v5 as b


where (@(a.z - b.z)) > 5


and st_distance(a.geom, b.geom) < 200
 
Subject Earth and Environmental Sciences
Bathymetry Points
Lake Victoria
Bathymetry
 
Language English
 
Contributor Krach, Noah
 
Type GIS Points