Today’s canal map of South Florida is the third I’ve shared. These recently created maps are the work of SFWMD’s Z.(Ken) Chen, Ph.D., GISP, Supervisor, Geospatial Mapping Services Unit, and his very talented team: Lexie Hoffart, Nicole Miller, and Erica Moylan SFWMD’s GIS.
Exploring these maps of Dr Chen and Team, in particular, allows one to fly with out an airplane! I am always surprised by what I see and learn. You may be too! Through knowledge we shall achieve a clean water future.
Words of Dr Chen satellite map:
Current Satellite Imagery
The satellite images are from Landsat data that are the most recent cloud-free (e.g. <10% cloud coverage) images over our areas of interest. The sensor on Landsat is called TM or Thematic Mapper. Therefore these images are usually called Landsat data or TM data. Because these individual TM images (or scenes) are processed by USGS following a standard Landsat imagery processing process, and exported to a standard imagery format, therefore it was not very technically challenging when we mosaicked or stitched them together. But the mosaicking was a very time-consuming process because imagery processing always requires a lot of computer time (i.e. CPU and GPU intensive) partially due to the fact of large file size of images as well as the nature of imagery processing. During the mosaicking process, we cropped out the black edges of the individual scenes and applied a limited tonal balancing to minimized the tonal contrasts between the individual scenes.
Today I am very excited to begin sharing maps created by SFWMD Supervisor of Geospatial Mapping, Dr Ken Chen, and team: Lexie Hoffart, Nicole Miller, and Erika Moylan. These maps allow us to “see” Florida in a way never seen before!
I will start first with the map entitled Current Canal Network of South Florida with Historic Imagery 1940 to 1953 (298-linework). This map is best viewed after you export the PDF to your desktop. In Safari this can be done by linking to SWMDCurrentCanalNetworkHistoricImages, then “File” and “Export as a PDF.”
Once downloaded to you desktop, you can zoom in and move up and down where you wish to go. What will you see? You will see the modern mapped canal network of South Florida atop hundreds of historic aerial photographs that have been stitched together. Incredible!
Tommy Strowd, former Assistant Executive Director of Operations, Maintenance & Construction at the SFWMD now Executive Director of the Lake Worth Drainage District eloquently states: “These maps are beautiful completed puzzles that clearly show probably the best photographic evidence of what the pre-drainage landscape looked like before the the C&SF Project and the vast system of secondary and tertiary drainage ditches were constructed.”
So this map juxtaposes Florida’s pre-C&SF Project drainage landscape to the canals that drain that remaining landscape today…
The current canal system includes the Primary System of the South Florida Water Management District, Works of the District; Other Canals Streams or Rivers; and the Secondary /Tertiary System including 298 Special Drainage District canals, and other canals, streams or rivers.
As an example, let’s zoom into St Lucie, Martin, and northern Palm Beach Counties. The pastel colors denote 298 Special Drainage Districts, some like the Lake Worth Drainage District go back to the 1913 General Drainage Laws of Florida. The Central and South Florida Project -what we think of when we think of the SFWMD-was constructed starting in 1948. Just a quick glance reveals the extensive wetlands that have been drained by the primary and secondary/tertiary systems. Wow! Now we can “see” how we drained the land and contemplate our water past as well as our water future.
What a great learning tool to understand and improve water quality!
To understand the creation and complexity of the maps I am including the following words of Dr Ken Chen Ph.D., GISP, Supervisor, Geospatial Mapping Services UnitInformation Technology Bureau, South Florida Water Management District. I had asked him to describe what was entailed with the historic imaging. Thank you to Dr Chen and Team whose talent, research, and time made these maps possible.
Historical aerials (1940 – 1953)
“Sources of historical aerials, especially 1940s and 1950s, are very scarce, especially for such a large area in South Florida. Therefore our focus was to get whatever we could find online regardless cloud cover or quality of images. As you know, all of those old images were recorded in an analog format (i.e. film or paper), instead of digital. Some (maybe all) of those films/paper images were later scanned and saved to a digital format and made available online. Scanning usually results in loss of imagery quality. For this canal map project, we were fortunately able to locate aerial index images (I would call them aerials index panels), after weeks of online research including data download and review. Each index panel displays a group of aerials in sequence over a specific area. For instance, say 200 images from #1 to #200 over an entire county. These index panels are usually used for aerial imagery management and archival purposes, just like a library index card for images. There is no information at all regarding how those index panels were created, but they are seemingly made via camera shooting or scanning of a group of stacked paper images or positive films. The index panels are simple graphics or pictures without any geospatial information, such as projection, coordinate system etc. The first step to process these index panels, prior to mosaicking, was to geo-rectify and inject geospatial information into the images. To do so staff needed to identify ground control points. It’s very challenging to identify those points in those very old images due to lack of apparent landmarks, e.g. road intersections. This is particularly difficult in the middle of nowhere across the vast wetlands in 1940s-1950s. So staff tried to use a very few of the intersections between rivers, canals and a few major roads to geo-rectify the panels and assigned appropriate geospatial information into them to make them georeferenced images. Then staff clipped each panel image to trim out the white or black edges before stitching all of them together for the majority of south Florida.
The original aerials were collected by the U.S. Dept of Agriculture. The aerials index panels were obtained from the Univ. of Florida’s Imagery Library. One thing to note – it’s very evident that there are strong image vignetting effects in the old aerials – bright in the center and getting darker toward the edges. That is an inherent optical artifact in the analog images and can not be corrected during the post processing.
This may be more than you asked for. I’m not sure if I have explained this clearly. To summarize it, this process can be simply illustrated in the following format:
Online search of available sources of data -> data download and review to accept or reject -> identify ground control points (GCP) in prep for image processing -> Using GCPs to georectify the index panels -> inject geospatial information into the panel pictures to make them georeferenced images -> remove the white/black edges -> Mosaick all georectified index panel images -> clip the mosaic to the district’s boundaries before use in the maps.
I forgot to mention the number of historical aerials we used to create the historical mosaic. We used totally 84 aerial index panels. Each panel consists of roughly 50+ to 200+ individual aerials, depending upon the geographic area each panel covers. I can’t get the exact number of aerials, my best guess the number would be ~7,000+-12,000.”