Reao Atoll FP - Finished . . . At Last!

Reao Atoll

Reao Atoll - ISS004 Image Mosaic (1:70,000)

Reao Atoll - EEVS Precision Map (1:70,000)

Reao or Natūpe is an atoll in the eastern expanses of the Tuamotu group in French Polynesia. The closest land is Pukarua Atoll, located 48 km to the WNW.

Reao is 24.5 km long and its maximum width is 5 km. The whole length of its north-eastern rim is occupied by a single long island. There is no navigable pass into the lagoon.

Reao Atoll's population is 344 inhabitants.

That is about it for Reao Atoll on the internet. There might be some scattered bits of information, but nothing of newsworthy significance. Why? It could be the location. Unlike many of the other atolls making up the Tuamotus that receive numerous pleasure cruisers, Reao Atoll is situated away from the normal cruising routes. In addition the lagoon has no entrance for sailing vessels making for percarious landings on and off of the main island.

Even with the geographical difficulties associated with Reao Atoll, I wouldn't mind visiting. The southern end of the atoll looks a bit on the wild side. If not real wild, it looks to be far from the population center of the island located on it's northern end. One could perhaps find an isolated small motu along the atoll's western edge. There are in the neighborhood of 50 motus along this edge of the atoll. I am certain one of these small motus could offer one a few days of solitude. If not a few days, for sure a few hours.

Now for a few comments on the map. First, the base imagery is from ISS004. I took 3 excellent images and assembled them into a mosaic of the entire island. I rotated the image about 37° to align it with the atoll's true alignment. I had created a shoreline of Reao Atoll a few years back, but had not saved the georectified image. All I had to work with was the island polygons which came from the ISS004 imagery. I used over 37 GCPs (ground control points) to georectify the ISS004 image mosaic. It wasn't until this weekend that I had both time and energy to complete my typical four vector layers - island polygons, vegetation polygons, shallow reef polygon and lagoon polygon. I completed all of the layers as Phil Mickelson was busy winning the Masters for the 3rd time.

P.S. - Later that day, I compiled my first OSM formatted vector file consisting of the island polygons. Ultimately my goal is to place my EVS copyright free vectors onto OpenStreetMap. That is another story for later time.

Marutea Atoll Nord FP - An Uninhabited Atoll...Kind Of

Marutea Atoll Nord FP

Marutea Atoll Nord FP - Landsat ETM S-07-15_2000 Image (1:150,000)

A portion of the Landsat ETM+ image looks great, the other portion is cloud covered. If I had only used the Landsat image to create my EVS precision map, it would have been an incomplete effort. Fortunately, ISS imagery helped to fill in the gap.

Marutea Atoll Nord FP - ISS006E37438 Image Modified (1:150,000)

First I had to rotate the ISS image and georectify it to my Landsat base image. I was able to do it after much tweaking of the ISS image it was positioned properly for my mapping purposes. Many of the coral heads, which I classify as shallow reef, were derived from the ISS image.

Marutea Atoll Nord FP - EVs Precision Map (1-150,000)

And here is the finished map! If one requires hi-res imagery, it can be found in Google Earth. Located at the channel leading into the lagoon are a few houses. I suspect they are used by coconut or black pearl harvesters. Although the island is uninhabited, people frequent the atoll doing the things that people do, harvesting resources.

Looking at the DigitalGlobe imagery found in Google Earth, large stretches of the island appear to be without a sand covering. It looks as if the island was washed over by a typhoon or a storm surge. Perhaps someone with first hand knowledge might share more about this uninhabited atoll...kind of.

Enjoy!

Anaa Atoll FP - Many Motus Surrounding a Shallow Lagoon

Anaa Atoll FP - Landsat ETM+ Image S-06-15_2000 (1:125,000)

Anaa Atoll FP - ISS006-E-34723 and 34724 Image (1:125,000)

Prior to beginning an EVS precision island mapping project, I scout for ISS imagery, especially ISS-006 imagery. Some excellent cloud-free images were captured during this mission. In the case of Anaa Atoll, Landsat ETM+ had some cloud issues. I downloaded, combined and georectified ISS imagery. Working with the Landsat image beneath the ISS image gave me excellent detail from which to create my finished EVS precision map.

Anaa Atoll FP - EVS Precision Map (1:125,000)

For me, the most interesting feature on this map is the shallow lagoon. It has a few deep areas, but is overall shallow with most underwater features within it close to the surface. The atoll has a permanent population of 435 people (2002 census) scattered between a main village and a couple of smaller settlements. According to the Wikipedia article about Anaa Atoll, the soldiers that lived on Anaa were an especially viscious group. In 1769, James Cook was the first European to sight the atoll.

This mapping project took about three weeks to complete using an on-again, off-again pace. Seems my life has gotten complicated between preparing for the new school year, watching my grandchildren, completing "honey-do's" and squeezing in map work late at night.

Enjoy!

Hikueru Atoll FP

Hikueru Atoll - Google Maps

Hikueru Atoll - Landsat Image S-07-15_2000 (1:70,000)

There are times Landsat ETM+ island imagery is obscured by clouds. That is when I go to plan ISS or International Space Station imagery. One is not guaranteed that cloud free imagery will be available, but that is where I search for quality imagery.

Hikueru Atoll - ISS Image ISS002-E-8866 (1:70,000)

In the case of Hikueru Atoll, ISS002 snapped some great cloud-free images of Tuamotu atolls. Hikueru Atoll is covered by the above image. Using the above two images I was able to create my finished map of Hikueru.

Hikueru Atoll - Other Precision Map (1:70,000)

This mapping is part of my on going effort to map the islands of the South Pacific at EVS Precision or better. Other Precision is always EVS Precision or better. The map was finished using Marplot mapping software.

Hikueru Atoll is covered by a brief article in Wikipedia. As of the 1988 census, 124 people live on Hikueru. They earn a living from copra, fishing and pearls. The atoll does have an airport, which can be seen in the ISS image, that was built in 2000.

Enjoy!

How To Digitize Shorelines Using ISS Imagery

My mapping target for the night, Takume Atoll. The Landsat image, S-07-15_2000, looks pretty good. Clouds obscure the northern motus. So how does this intrepid mapper solve this digitizing problem.

First, I checked out DigitalGlobe's imagery in Google Earth. The northern section of the atoll is covered with cloud-free hi-res imagery. Since I am looking to possibly explore commercial opportunities for my EVS precison island maps, DigitalGlobe imagery is a "no go".

I visited the Gateway to Astronaut Photography and poked around to see what imagery was available for this atoll. It turns out during the ISS006 mission, this atoll was photographed. I downloaded both photos and went about putting them together.

I pieced the two images together using Irfanview and ImageForge. I loaded the northern section first and placed the southern section on top of it. I had to do a small stretch to make the southern image fit onto the northern section.

I trimed the modified image and saved it. Now I have to tilt it at the proper angle to better georectify the image.

Using a measuring feature in Global Mapper, I was able to determine that the atoll is at a 42° angle. Now I needed to tilt the image 42°. Irfanview allowed me to tilt the image the requisite degrees.

I used Global Mapper's georectifying module to georeference the tilted image. I selected a rectification routine called Triangulation which requires 5 GCPs. 3 GCPs were selected in the northern section and 2 GCPs were selected in the southern section.

And there is the georectified Takume Atoll ISS image.

I used the ISS image to digitize the cloud covered northern motus. Once they were completed, I tricked the top image (ISS) to complete digitizing the balance of the atoll.

I used a translucency option and converted the ISS image to 70% translucency. This allows the underlying image, primarily their colors, to show through the top image. I used this setup to complete digitizing the remaining shorelines.

Here is the finished northern section of Takume Atoll. All of the cloud covered motus are mapped using ISS imagery. Pretty cool, huh?

Enjoy!

Reao Atoll FP - The Finished Map

Reao Atoll - ISS004-E-12987, 12988, 12989 Images (1:100,000)

Reao Atoll - Other Precision Map - Source ISS004 Images (1:100,000)

This is my finished shoreline map of Reao Atoll FP. The imagery covering this atoll is of sufficient detail that other layers of information can be digitized, if I wish. For now I just want to complete shorelines within the Tuamotus at EVS precision or better.

Enjoy!

How To Map Motus

View Larger Map

Zoom In to See Pukaruha and Reao Atolls

Reao Atoll FP - ISS004-E-12987, 12988, 12989 Images Modified (1:75,000)

For whatever reason Landsat ETM+ does not have a mosaic that covers Reao Atoll. Google Earth has Landsat imagery, but no imagery for this area at the NASA site where I download my Landsat ETM+'s. As I am making all of my maps without using DigitalGlobe imagery, because one day I might want to sell my shorelines, I must locate other imagery sources. The International Space Station (ISS) is a source of sometimes excellent imagery. And, in fact, ISS004 has 3 cloud-free, highly detailed images covering Reao Atoll, my current target project.

I downloaded, modified their sizes, constructed a "whole atoll" mosaic, rotated the image to align it with my base island shoreline vectors (NGA PGS vectors) and georectified this image using 7 GCPs.

Reao Atoll FP - Other Precision Mapping on ISS Images - Finished Motus (1:40,000)

Reao Atoll FP - Other Precision Mapping - Finished Motus (1:40,000)

Once I had a georectified image, my digitizing could proceed. I decided to map motus first, thus the title of this post. Motu mapping is quick, repetitive and gives one a sense of completion. Each motu is actually a small island. Reao Atoll will ultimately be made up of a 100 or more islands. The two above images show the results of about 2-hours worth of digitizing. I always strive for EVS precision, Landsat ETM+ resolution or better. This imagery allows me to exceed EVS precision. For mapping quality purposes, I label it as Other precision and label it's Source attribute as ISS-Hi Res. I have completed 58 Other precision island polygons. Let's look at the challenges one encounters as they map motus.

Reao Atoll FP - Other Precision - Digitizing Motu (1:10,000)

First, I am working at 1:10,000 scale. At this scale, I am able to maintain sharp feature clarity. In addition, this resolution allows me to make consistent shoreline determinations that will work with the scale of my finished map, between 1:50,000 to 1:25,000. My mapped shorelines consist of actual or suspected (based on color) above-water features. Sounds easy enough to consistently identify, but it isn't. After mapping a few thousand motus, I have learned to make a color(s) to shoreline decision and rigourously adhere to that definition. In imagery, color is god.

In the Reao Atoll image, the motu shorelines are identified as a white sand color. Having studied enough hi-res 1-meter imagery of reefs and motus, I know that between motus are features called hoas. These serve as channels allowing water to flow in and out of the lagoon. Eventually, these hoas fill up with coral rubble and sand, vegetation takes root and motus join motus to form a continuous land ring around a lagoon. Given enough time, the lagoon quite often fills in and, sea level cooperating, a flat island forms where an atoll once stood. Using my white sand color as my motu shoreline, I began digitizing.

Reao Atoll FP - Other Precision Mapping - Finished Motu (1:10,000)

If I do a good job, my project consists of a series of motu shorelines. The digitizing is monotonous, eye-straining and lately, my feet hurt because my chair is uncomfortable. But the finished map is what I work for. I'll share it with you when I've finished. Until then...

Enjoy!

How To Digitize Cloud-Obscured Shorelines

Raivava'e Atoll - EVS Precision Map on Landsat S-06-20_2000 (1-55,000)

As most of my regular readers know, the bulk of my mapping work is derived from Landsat ETM+. My primary reason for using Landsat ETM+ as base imagery is consistency of product. Typically, anywhere on earth this imagery is freely available, virtually cloud-free and consistently resolved to 14.5-meters per pixel. Great for my worldwide island mapping work. Plus, there are minimal copyright issues when using this imagery. All that is asked is that you credit the source imagery. Did I say "virtually cloud-free"? That is everywhere but in humid climates, in other words in and around islands. Oh, well, it is merely a challenge that the accomplished mapper learns to work around.

The above image is an example of cloud-obscured island imagery. Most of Raivava'e Atoll is visible, but those areas not visible are significant. How does one resolve these areas using copyright-free data (credit source data)? If I am unable to secure Landsat 1990 imagery, which quite often enables one to resolve cloud-obscured areas, I go to Shuttle photography. Specifically, searching for ISS (International Space Station) imagery.

Raivava'e Atoll - EVS Precision Map on ISD_ISS001-375-13 Modified (1-55,000)

Raivava'e Atoll has two images that show the atoll with virtually no clouds. These images are sufficiently large enough that one is able to zoom into and digitize features. First, however, the ISS image must be georectified. Global Mapper allows me to georectify ISS imagery using my Landsat base imagery. In georectifying this ISS image, I used 7 GCP's to ensure the ISS image lay precisely on top of the Landsat base image.

Raivava'e Atoll Outlying Motus - EVS Precision Map on Landsat S-06-20_2000 (1-10,000)

Raivava'e Atoll Outlying Motus - EVS Precision Map on ISD_ISS001-375-13 Modified (1-10,000)

Beginning with the cloud-obscured Landsat image above, I digitized as much of the atoll as possible. The cloud-obscured portions were identified and designated for further work. Visiting Shuttle photography, I found 2 cloud-free images of Raivava'e Atoll. I selected ISD_ISS001-375-13 as the better of the two images. I rotated it and cropped to the atoll. Using this modified ISS image, I was able to complete digitizing the cloud-obscured shoreline. When all else fails, I use WVS shorelines. They are crude compared to EVS precision, but they work.

I use red shorelines to designate EVS precision derived from Landsat base imagery. The green shorelines are designated as Other precision. The source for all Other precision shorelines in my Raivava'e Atoll map is the ISS imagery.

My EVS precision island map of Raivava'e Atoll is complete and I was able to digitize all shorelines in spite of clouds. Pretty cool, huh?

Enjoy!

Comparison - Google Earth Georectification vs Landsat ETM+ Georectification. Who is Right?

My previous post elicited a question asking which image was georectified properly and wondering if I had verified the projection. I am a trusting soul and if, in the instance of my previous post, the NGA PGS vector coordinates are what I used to georectify the ISS image. I am reasonably confident the ISS image fit precisely into the NGA PGS vectors. Ultimately the ISS image I fashioned used a Geographic (latitude/longitude) projection with WGS-84 datum.

This evening I loaded the Landsat ETM+ orthorectified mosaic N-20-10_2000, which includes Isla Blanquilla, into Global Mapper. It loaded quickly. I zoomed into Isla Blanquilla at a scale of 1:62,5000, which was the scale of my final map project. I then loaded the ISS georectified base image of Isla Blanquilla on top of the Landsat image. It is right on! A precise fit. However, yesterday when I attempted to create an overlay of the ISS image in Google Earth and after spending 15-minutes stretching and twisting the image, it never quite fit. It was alway alittle off.

Google Earth to Landsat ETM+ Georectification Offset

This evening, I recorded the lat/lon location of three relative ground control points within Google Earth and in Global Mapper's Landsat display. They each showed the same image of Isla Blanquilla and supposedly at the same location. Each relative ground control point was easily discernible. After recording lat/lons for each point and determining the difference, it seems someone is off anywhere between 2-meters and up to 63-meters for this single island. So, who is it? Who has misplotted this island? Is it Google Earth or Landsat ETM+? Care to guess?

Enjoy!

Isla Blanquilla VE - ISS Island Image Transformed into EVS Precision Map

Isla Blanquilla - ISS015-E-7771 Image

A few days ago Earth Observatory carried this image of Isla Blanquilla and an interesting article about this small island located NE of Caracas Venezuela. Granted, if you are a US citizen, it is probably not your first choice to visit on a leisurely vacation due to the strained relations between our two countries, but the ISS image is pristine and details are mappable compared to the partially cloud-obscured Landsat ETM+ image. DigitalGlobe has never snapped a pic of this island either. So, I made do with the ISS image and created my map over a 4-hour period.

Isla Blanquilla - ISS015-E-7771 Georectified Image (1:62,500)

In order to use any non-georectified imagery, one must georectify it. I use Global Mapper to georectify. I loaded NGA PGS shorelines of this island (Region 14). These shorelines are very close to Landsat ETM+ shorelines. I selected 4 easily definable points on both my loaded shoreline line file and on my ISS image. It took about 10-minutes, with most of the time spent watching TV. Once the image was georectified, I began the task of digitizing the island shoreline, lower beach, upper beach, bare island, hi-low vegetation, airfield and the shallow reef surrounding the island.

Isla Blanquilla - EVS Marplot Map (1:62,500)

Once the digitizing was completed, I imported the completed layers into Marplot, where I still do much of my preliminary map construction. I am just used to working with it. I defined each layer and assigned it to pre-existing EVS layers. I did a quick layout of map titles, legend, scale and north arrow. Done!

At this point, I typically post. One day when I am given the opportunity and the time, I will "fancy" up my map using ImageForge prior to posting. Until that day arrives, this is as good as it gets.

Enjoy!

Little Sitkin Island US - These are "WOW" Images

Little Sitkin Island - View North (ISS Image Mosaic)

Little Sitkin Island US - A GE Tour

I'm not a Google Earth (GE) mashup person. The only way I could think to share my work posted in Google Earth was using screen shots. I am making use of Flickr slideshow feature. It will give you an idea on how a brief tour in GE might be.

The two images that makeup my overlay are from two ISS005 Images (18288 & 18289). I patched them together to create this virtually cloud-free image of Little Sitkin. Cloud-free and the Aleutians is a weather anomoly. If you do get a clear day, the islands are often shrouded in snow. These images are exquisite for clarity of ground detail. The images gets their 3D effect from the underlying data (SRTM/DEM) in GE. The western shoreline has been stretched to accomodate the underlying SRTM/DEM data. Consequently, the lat/lon's for that shoreline are off by a few hundred meters. If you want to make a map, you will need to get in touch with me and I'll send you a GEOTIFF image of the island. With that you can make a map.

The photos were taken during a research trip in 2005. The photographer is unidentified. Images are courtesy of AVO/U.S. Geological Survey. Please cite the photographer and Alaska Volcano Observatory / U.S. Geological Survey when using these images.

Follow this link and you can take the tour in GE.

View Little Sitkin Island on Google Maps

Enjoy!