EVS-Islands

Cook Islands - Landsat ETM+ Coverage

I have been very busy digitizing islands. In fact, I have just completed digitizing over 3,000 large and small islands making up the western portion of the Solomon Islands. I'm currently digitizing island shorelines in Papua New Guinea. All of this work is being done at EVS precision - using Landsat ETM+ base imagery and digitizing shorelines at a scale between 1:25,000 up to 1:50,000. Some of you have reminded me that because Landsat ETM+ is typically 14.5-meter resolution that digitizing at the scale I work at is overkill. After spending close to 3-years working with 14.5-meter resolution imagery, the maps I am able to produce work quite well. I wouldn't want to sail into a lagoon using only ETM+ imagery, but I could do excellent advance planning and rough navigation using maps derived from this imagery. I know my maps are often far superior in shoreline validity when compared to some of the very old nautical charts still in use today.

Anyway, this is supposed to be about green dots on a deep black sea. In between work on the Solomons and Papua New Guinea, I completed EVS precision mapping of the Cook Islands. The first image in this post struck me. It took seven Landsat ETM+ mosaics to cover the Cook Islands. If you study the above image at full size, almost all of these very small islands are impossible to see. Yet, they enable countries, like New Zealand, to claims (EEZ) enormous chunks of liquid real estate. These very small islands play a significant role in the distribution of world resources. Interesting.

Cook Islands - Marplot Map with 25-km Ocean Masks

The Marplot map of the Cook Islands shows their distribution more clearly. They are scattered about within a peculiarly shaped border, that is if one finds rectangles peculiar. Actually, their EEZs would spill outside of their international border. I'm not sure if the border serves to limit their 200-NM EEZs. If that is the case, too bad for New Zealand and the Cook islanders.

Penrhyn Atoll CW - Landsat S-04-05_2000 Image (1:125,000)

Just to confirm that there are islands located in this broad expanse of black ocean, here is one of them, Penrhyn Atoll. It has a classic atoll shape with a lagoon full of near surface coral heads. I have not researched Penrhyn as I was in a digitizing mode when I worked on it, not in an investigative one.

Penrhyn Atoll CW - EVS Precison Island Polygon Map (1:125,000)

This is my EVS precision map of Penrhyn Atoll. It is a solid shoreline depiction. My customary mapping effort of an atoll would include a number of additional layers of information - reefs, beaches, vegetation. As my client requires only shorelines, I digitizied and mapped the island's above-water shoreline and portion of it's awash reef. Again, it is a solid shoreline mapping effort and one that I will revisit to complete the other layers of information I would typically map.

I am still here, just not able to post as often as I would like. When I finish my paying mapping project (Whoopee!), I will share many, many, many more islands. Until then...

Enjoy!

Labels: Cook Islands, digitize, EVS Precision, Landsat ETM+, Papua New Guinea, Solomon Islands

Posted by Mr Minton at 4/30/2008 08:22:00 AM | Permalink | Comments | links to this post

Aitutaki (18˚54'S., 159˚46'W.), the farthest NW of the Lower Cook Islands, lies about 51 miles WNW of Manuae Atoll. The island, about 4 miles long in a N-S direction, is located at the N end of a reef which is a fringing reef on its N extremity, but becomes a barrier reef farther S. A number of small islets, from 6 to 18m high and covered with trees, stand on the barrier reef; also, some low cays on the E side of the reef break heavily.

Aitutaki rises to a height of 119-meters in the N part. A light is situated on this peak. There are some conspicuous rocks, 11.6m high, off a point on the W coast about 2 miles SSW of the N extremity of the island. A house with a conspicuous silver-grey roof stands near the coast, about 0.4 mile SSE of the conspicuous rocks, and 0.6 mile SSW of the house there is a church with a conspicuous red roof.

Motikitiu, a small islet, is located near the SE extremity of the barrier reef 4 miles SE of Aitutaki; Maina, a small islet, is located near the W extremity of the reef, 5.5 miles WNW of Motikitiu.

(SD Pub-126)

---

Group: Archipelago: Southern Cook Islands Country: Cook Islands Region: Oceania 16 Lat: 18.88º S Long : 159.74º W Area: 16.5 sq. km Altitude: 124 m Shoreline: 24.1 km (scale 1:250000) Coastal Index: 1.4606 Submerged area <100 m: 0 sq. km Reef area: 0 sq. km Lagoon area: 66 sq. km Depth to nearest land: 4000 m Nearest island: 100 km Group: 700 km Nearest continent: Australia Distance: 5000 km Isolation Index: 107 ISLAND TYPE: volcanic, almost atoll Natural Protection Indicator: 0 GEOLOGY/SOILS: Volcanic island to one side of large lagoon which is silting up (mostly under 4.5 m, maximum 10.5 m depth), 13 low coral islands (2.2 km}) on triangular reef CLIMATE: tropical rainfall 1900 mm CATASTROPHIC THREATS: cyclones Threat Indicator: 1 ECOSYSTEMS: Lowland rain forest, disturbed lowland vegetation; coconuts and scrub on coral islets; fringing reef, barrier reef 600-1000 m wide, lagoon with patch reefs (CRD) Forest Number of Ecosystems - Terrestrial: 4 Marine: 4 Percent shoreline: Coral Reef: 99% Mangrove: 0% SPECIES OF CONSERVATION INTEREST: Marine life: 28 coral genera Birds: Vini peruviana (Tahiti Lorikeet) introduced, Rare (RDB) Species Richness Indicator - Terrestrial: 1 Marine: 0 HUMAN OCCUPATION: Inhabited Population: 2904 (1960) Density: 176.0 persons/sq. km Growth Rate: 1.1%/yr Increasing slowly Major Human Activities: agriculture, tourism,, fishing and aquaculture HUMAN IMPACTS: Much of land cleared for agriculture Habitat: scattered villages Urban Pop: 0 Urban Indicator: 0 Accessibility: airport Conservation support: legislation DATA RELIABILITY: good Data Rel. Indicator: 3 HUMAN IMPACT INDEX HI: 7 CONSERVATION IMPORTANCE INDEX CI-Terrestrial: 7 Moderate CI-Marine: 4 Low REFERENCES: Good SPOT satellite images of Aititaki (Lubersac et al., in press) Last updated: 06/05/89

---

This was not a particularly difficult project to complete. It was just time consuming. It took about 5-hours of work to finish. I am surprised that the Sailing Directions had so little information about this island. It usually has quite alot to say about islands of this size, especially when they have a port listed in the World Port Index.

You will note that I have not attempted to edit the UNEP Islands information. I am awaiting word from the gentleman who controls access to the data. I need to secure permission to post edited information.

There is a great resource available online for this island. The publication is the Smithsonian's Atoll Research Bulletin No 190. The link I have given you will take you to the index. Find No 190 in the list of pubs titled "Almost-Atoll of Aitutaki: Reef Studies in the Cook Islands, South Pacific". The research was conducted in the early 1970's. The pub contains some excellent maps of the individual motus. If you have an interest in this island, this is the pub for you.

Enjoy!

Labels: atoll, Cook Islands, EVS, island, Landsat, map, Marplot, Pacific, Survivor

Posted by Mr Minton at 10/19/2006 12:30:00 PM | Permalink | Comments | links to this post

Suwarrow Atoll (13˚16'S., 163˚06'W.) consists of several wooded islets lying on a barrier reef which encloses a lagoon. Anchorage Island on the NE side and High Island on the W side of the island are covered with coconut trees from 18 to 25m high; they are easily recognized. The barrier reef shows a little above HW. It is dangerous to approach the reef on its S or SE side unless the weather is clear. The N side projects to a sharp point; on the E side of it, there are some islets covered with brush.

Northeast Reef lies about 0.5 mile E of Anchorage Island and forms the E side of the entrance. East Reef lies 0.3 mile E of the S extremity of Anchorage Island, and South Reef lies about 0.2 mile SSW of East Reef. South and East Reefs can be distinctly seen from 3 miles.

The coast in the vicinity of the passage is said to be dangerous to approach at night due to irregularities in the line of the barrier reef. The lagoon entrance is just E of Anchorage Island. A vessel, with a draft of 4.6m, can use the channel between Anchorage Island and South Reef, but caution and local knowledge is necessary. Currents in the lagoon entrance are irregular. Rates on the flood reach 0.5 to 1 knot, while the ebb flows at rates of 2 to 3 knots. At the anchorage within the lagoon, the ebb current starts about 1 hour 30 minutes before HW.

Anchorage.—Anchorage, unsafe in N weather, may be taken inside the lagoon, 0.2 mile off the W side of Anchorage Island, in a depth of 33m.

(SD Pub-126)

---

Suvorov Atoll (aka Suwarrow) is made up of many little islands scattered around the barrier reef. The islands are low to the water and are not safe in storm tossed seas. According to sailors that write on their blog sites, the islands in the north have a caretaker that ensures the safety of the islands.

This was the home of Tom Neale, a guy who decided to get away from it all. He escaped to Suvorov and stayed "away from the world of man" ("Joe vs The Volcano"). He stayed on the island two separate times and loved it, both times. The above link will give you more detailed information.

---

This island took about 6-hours to complete. I divided the work into two sessions. The reefs were fairly complicated to digitize. The finished map consists of 14-different layers of information. The island map turned out quite nice. The finished map was as much fun to admire as the process to complete it was.

Enjoy!

Labels: atoll, Cook Islands, EVS, island, Landsat, map, Marplot, Pacific

Posted by Mr Minton at 10/12/2006 10:25:00 PM | Permalink | Comments | links to this post

Pukapuka Atoll (10˚55'S., 165˚50'W.) lie about 42 miles NNW of Nassau Island. They consist of Pukapuka, the farthest N; Motu Ko, 3 miles S of Pukapuka; Motu Katava, 1.5 miles NW of Motu Ko; and several smaller islets and sand cays. A sand cay lies at the W end of a reef, 3 miles W of Motu Katava. The islands, islets, and sand cays lie on or within the barrier reef, which surrounds a shallow lagoon.

The barrier reef is unbroken and there is no access to the lagoon for other than small boats. On its W side the barrier reef is always awash; its S side is awash at LW, and its E side is partly awash and partly dry sand. The sea breaks over the sunken reef which extends W from Motu Katava.

Pukapuka is densely wooded with coconut and other trees; some reach a height of 24m. The island is bordered on its N and W sides by wide, flat reefs, and the surf beats heavily on the narrower reef on the weather side. Three villages are situated on the S side of the island near the lagoon; a large church and a school are situated in one of the villages. The Resident Agent lives on Pukapuka.

Motu Ko, at the SE end of barrier reef, is flat and sparsely wooded; the tops of the trees rise to a height of 30m. An aviation runway is situated on the S side of Motu Ko.

Motu Katava is densely wooded in its W part. The trees on the W side rise to a height of 38m, and the coconut palms on the E side rise to 24m.

The current sets strongly onto the E side of the Danger Islands.

The current across the reef extending W from the islands is dangerous. It runs S during the ebb and N during the flood, attaining a rate of 3 to 5 knots. This reef is said to break in deep water even on a calm day.(SD Pub-126)

---

I have spent the last 3 evenings working on Pukapuka Atoll. The project began as a test of the Protype Global Shoreline map file for Pukapuka Atoll. The PGS files, although a tremendous improvement over WVS, are too coarse for a well-done EVS island.

The EVS map for Pukapuka Atoll is a very well done product. I love the work that I was able to do on the various reefs that are part of this atoll. I did use a shuttle image (see above) to resolve shoreline that was cloud-obscured. This is one of my best maps to date. Air Rarotonga has information on Pukapuka Atoll.

Enjoy!

Labels: atoll, Cook Islands, EVS, island, Landsat, map, Marplot, Pacific

Posted by Mr Minton at 6/17/2006 03:22:00 PM | Permalink | Comments | links to this post

So, I decided to test the PGS vectors (red lines) against Pukapuka Atoll, Cook Islands digitized at EVS quality. There is a cloud issue on one of the motus. Fortunately, the clouds were not a problem with Motu Ko. I tried to digitize by moving vectors to trace the visible shoreline. I moved more vectors then I didn't. At least 70%+ of the vectors had to be moved to track the visible shoreline. The moves were slight, less than a few millimeters which equals 10's of meters on the ground. Some of the vectors traced reefs that were classified as shorelines (northern part of Motu Ko).

The PGS vectors are close, but no cigar. For EVS quality the PGS vectors require a great deal of adjusting. To produce EVS islands, I need to digitize off of the Landsat image. So, I will keep doing what I do best, making EVS shorelines.

Enjoy!

Labels: Cook Islands, EVS, island, Landsat, map, Marplot, PGS

Posted by Mr Minton at 6/14/2006 11:18:00 PM | Permalink | Comments | links to this post