QINSY

QINSy ( Quality Integrated Navigation System ) is a hydrographic data acquisition, navigation and processing software package.


QINSY for Multibeam
QINSy is an integrated navigation system software package used extensively worldwide for acquiring and processing multibeam data.
Online - Navigation Display

The primary philosophy behind QINSy is to save time in processing, and the possible need for re-survey, by providing tools for real-time qualification of the raw data and on-the-fly correcting for offsets, motion, sound velocity refraction and height, to produce “final” xyz soundings as the survey proceeds.

online qc
An array of real-time quality assurance tools and displays are available to the online surveyor who is arguably in the best position to determine if collected data meets survey specifications. In addition to displaying the raw uncorrected multibeam data, the Swath Display shows the data fully corrected for motion, refraction and height.

sounding grid
A multi-layered “sounding grid” shown in the Navigation Display is populated with corrected soundings on-the-fly giving the surveyor a complete view of what has been surveyed. Sounding grid data attributes like the “95% confidence level” and “hit count” provide real-time quality assurance of collected data. Backscatter and/or sidescan/snippets imagery data is written to another layer of the sounding grid. Importing of a design DTM and/or previous survey allows real-time monitoring of DTM differences.

DTM files
In addition to gridded data, QINSy produces various other DTM files as well. Most well-known is the point cloud QPD file, opened directly in the QINSy Processing Manager and in Fledermaus to clean and validate the multibeam data.
               
calibration
To produce valid real-time DTMs, care must be taken during mobilization to measure offsets and perform calibrations, including calculation of the multibeam mounting angles. The slightest error in the mounting angle can influence the end result of the multibeam data. QINSy provides an automatic multibeam calibration routine, often referred to as the “patch test”.

preparation
If due care is taken at the outset to configure QINSy with offsets, mounting angles, SVPs and height settings, the many different displays can be used to their full potential to quality assure the incoming data and the computed results. With these QC tools the surveyor has full control of his data and is always aware of what is going on during the survey with the result that the recorded data is of high quality.

pre-cleaning
Data pre-cleaning during acquisition is possible if the surveyor activates certain clipping filters and de-spiking methods. No data is lost since all the raw data are stored in database files and/or XTF files and all results data are stored in QPD files, which are qualified with flag attributes consequent to pre-cleaning tests.
Processing - Quick Profile

processing
XYZ data is cleaned and processed using the QINSy Processing Manager and/or Fledermaus. One of the main features in the Processing Manager is the navigation surface, which is a dynamic grid that updates itself as soon a modification to one or more of the QPD files is done.

Source : QPS

Shuttle Radar Topography Mission (SRTM)


Shuttle Radar Topography Mission (SRTM) adalah data elevasi resolusi tinggi pada skala global kecil yang merepresentasikan topografi bumi dari 56oLS hingga 60oLU untuk menghasilkan database bumi dalam bentuk topografi digital dengan cakupan global (80% luasan dunia). Data SRTM adalah data elevasi muka bumi yang dihasilkan dari satelit yang diluncurkan NASA (National Aeronautics and Space Administration).


Data yang dihasilkan memiliki resolusi spasial sebesar 3 detik (setara ≈ 90 meter) dan menurut Ozah and Kufoniyi (2008) data SRTM 90m ini memiliki akurasi vertikal lebih kurang 7.748 sampai 3.926 meter.

Nilai ketinggian pada SRTM adalah nilai ketinggian dari datum WGS1984, bukan dari permukaan laut, tapi karena datum WGS1984 hampir berimpit dengan permukaan laut maka untuk skala tinjau dapat diabaikan perbedaan di antara keduanya.

SRTM dihasilkan dari penyiaman gelombang radar dengan teknik interferometri. Teknik interferometri radar adalah sebuah cara penyiaman muka bumi dengan dua posisi sensor radar yang berbeda tempat. Pada wahana pengambilan data SRTM ini, jarak rentangan dua sensor radar ini sejauh 60 meter, dimana satu sensor berada dalam wahana, dan sensor lain berada pada ujung rentangan di luar wahana. 

Gelombang radar dimanfaatkan untuk pengambilan data ini karena memiliki kelebihan, diantaranya adalah perekaman dapat dilakukan pada siang ataupun malam hari. Disamping itu gelombang radar dapat menembus tutupan awan. Dengan demikian, perekaman data SRTM tidak terpengaruh oleh keadaan cuaca setempat.  

Wahana SRTM membawa dua panel dengan saluran C dan Saluran X. Peta topografi global dari bumi disebut dengan Digital Elevation Models (DEMs). DEMs ini terbuat dari data radar saluran C tersebut. Data ini diolah oleh Jet Propulsion Laboratory dan didistribusikan melalui USGS EROS Data Center. Data saluran X digunakan untuk menghasilkan DEMs dengan resolusi yang lebih tinggi. Data SRTM dari saluran X diolah dan didistribusikan oleh German Aerospace Center.

Data SRTM dapat diunduh secara gratis pada situs cgiar-csi. SRTM NASA menyediakan data elevasi yang melingkupi 80% permukaan bumi. USGS menyediakan data tersebut secara gratis.

Kelebihan SRTM

*)Free Data
*)Format Data Digital (HGT, ASCII, atau GEOTIFF) sehingga kita bisa  mengkonversi data ke format yang kita inginkan.
*)Resolusi horizontal (yang bisa kita download untuk Indonesia) adalah 90m. Tentu saja dengan resolusi ini SRTM tidak bisa digunakan untuk pemetaan secara detail melainkan untuk pratinjau data.

Kelemahan SRTM

Dalam pengambilan data menggunakan RADAR, antara pesawat dan obyek harus tidak terhalangi. Untuk daerah yang bergunung hal ini sangat sulit dilakukan. SRTM memiliki 0.2% data yang tidak terliputi di muka bumi karena berupa pegunungan. Beberapa teknik telah dikembangkan untuk menutupi kekurangan ini. Salah satunya adalah dengan menggunakan algoritma otomatis dengan SRTM Filler.

Akuisisi Seismik Laut

Tujuan utama dari suatu survei seismik adalah melakukan pengukuran seismik untuk memperoleh rekaman yang berkualitas baik. Kualitas rekaman seismik dinilai dari perbandingan kandungan sinyal refleksi terhadap sinyal gangguan (S/N) dan keakuratan pengukuran waktu tempuh  (travel time) gelombang seismik ketika menjalar dalam batuan.
Eksplorasi seismik dapat dikelompokkan menjadi dua, yaitu : Eksplorasi prospek dangkal dan eksplorasi dalam. Eksplorasi seismik dangkal (shallow seismic reflection) biasanya diaplikasikan untuk eksplorasi batubara dan bahan tambang lainnya. Sedangkan ekplorasi seismik dalam digunakan untuk eksplorasi daerah prospek hidrokarbon yaitu minyak dan gas. Masing-masing dari  kegiatan tersebut menuntut resolusi dan akurasi yang berbeda dengan teknik lapangan yang berbeda pula.
Akuisisi data seismik laut 2D dilakukan untuk memetakan struktur geologi di bawah laut dengan menggunakan beberapa peralatan antara lain: 

- Streamer, 
Streamer yang dilengkapi dengan hydrophone, ADC (Analog to digital converter dan bird yang berperan untuk mengatur posisi dan kedalaman streamer). Diameter streamer sekitar 7 cm dengan panjangnya bisa mencapai 10km. Bagian hitam dari gambar ini menunjukkan perangkat ADC.




- Bird,
Berfungsi mengatur kedalaman dan posisi streamer.


- Air gun,  
Tekanannya bisa  mencapai 2000psi. Bagian ’air gun’ adalah selinder logam yang menggantung padanya.


Selain itu ada beberapa perlengkapan survei seismik lainnya.


Dalam praktiknya akuisisi seismic marine terdiri atas beberapa komponen: kapal utama, gun, streamer, GPS, kapal perintis dan kapal pengawal dan kadang-kadang perlengkapan gravity (ditempatkan di dalam kapal) dan magnetik yang biasanya ditempatkan 240 meter di belakang kapal utama (3 meter di dalam air)


Didalam kapal utama terdapat beberapa departemen: departemen perekaman (recording), navigasi, seismic processing, teknisi peralatan, ahli komputer, departemen yang bertanggung jawab atas keselamatan dan kesehatan kerja, departemen lingkungan, dokter, juru masak, dan kadang-kadang di lengkapi dengan departemen survey gravity dan magnetik, dll. Jumlah orang yang terlibat dalam keseluruhan operasi berjumlah sekitar 40 orang.



Untuk menjaga hal-hal yang tidak diinginkan, selama operasi ini disertai pula dua buah kapal perintis (chase boat) yakni sekitar 2 mil di depan kapal utama. Selain bertanggung jawab membersihkan lintasan yang akan dilewati (membersihkan rumpon, perangkap ikan, dll) , kapal perintis bertugas untuk menghalau kapal-kapal yang dapat menghalagi operasi ini. Selain itu di belakang streamer, terdapat juga sebuah kapal pengawal.

Operasi akuisisi data seismik memakan waktu dari mulai beberapa minggu sampai beberapa bulan, tergantung pada 'kesehatan' perangkat yang digunakan, musim, arus laut, dll.

Mengingat mahalnya operasi data akuisisi (mencapai 150 ribu dollar per hari, dalam operasi 3D bisa mencapai 250 ribu dollar per hari!) maka Quality Control dari operasi ini harus betul-betul diperhatikan, seperti apakah semua hidrophon bekerja dengan baik, apakah air gun memiliki tekanan yang cukup, apakah streamer dan air gun berada pada kedalaman yang dikehendaki, apakah feather tidak terlalu besar, dll. 

Beberapa parameter geofisika yang dipakai dalam akuisisi marin adalah sbb (contoh):
Record length: 9500ms
Sample rate: 2ms
Start of data: 50ms
Low cut filter: 3 Hz/ 6dB
Hi Cut filter: 200Hz @ 370dB / Octave
Tape format: Demux SEGD rev 1, 8058
Polarity: first break is negative
Shot point interval 25 m
No of streamer: 1
Streamer length: 8100m
Number of channels: 648
Group interval: 12.5 m
Operating depth: 7 m +/- 1m
Offset CSCNG (inline) 125m (center of source to center of near group)
Array volume: 4140 cu inc
Operating pressure: 2000 psi +/- 10%
Array configuration: 3 strings (each string = 9 segments)
Array separation: 15 m
Source depth: 6m +/- 1m
Center source to nav. mast: 185m



Navigasi bertugas untuk memastikan bahwa akuisisi data seismik berada pada lintasan yang dikehendaki. Disamping itu mereka juga memberikan informasi tentang feather akibat arus laut yang biasanya diterima dibawah 10° dan juga meminta kapten kapal mengatur kecepatan kapal, yang biasanya dibawah 5 knot.



 

Type of Offshore Rigs


The earliest offshore drilling was limited to coastal oil deposits that were accessible from piers, but oil companies today can choose from a variety of elaborate methods, letting them drill almost anywhere at almost any depth. From roving, computer-controlled contraptions to giant "spar" platforms held up by 10,000-foot poles, today's deepwater rigs are going far beyond anything their offshore forefathers could have imagined.

Such engineering wonders also come with big risks, however, as demonstrated by the 2010 Deepwater Horizon explosion, which killed 11 people and launched a torrent of oil into the Gulf of Mexico. Anything from human or mechanical error to corrosion, methane bubbles or earthquakes can spiral into a runaway disaster when drilling for oil offshore, and the struggles to control the Deepwater Horizon spill highlighted the difficulty of doing anything 5,000 feet deep in the ocean. 

But with potentially vast oil reserves located on North America's Outer Continental Shelf, and the United States still leading the world in oil consumption at 19.5 million barrels a day, oil companies and offshore-drilling advocates argue that extracting oil from the ocean is economically vital and environmentally safe. There are currently about 4,000 offshore drilling rigs and production platforms in the Gulf of Mexico, and under the Obama administration's new offshore energy strategy, more may soon appear off the North Slope of Alaska and even the U.S. East Coast. 

Oil-drilling technology is constantly improving, and some rigs combine elements from different models to achieve specific abilities. But in general, the major types of offshore oil rigs include the following:

Fixed platform: Anchored directly into the seabed, fixed-platform rigs consist of a tall, steel structure known as a "jacket" that rises up from the ocean to support a surface deck. The jacket provides the rig's sturdy base and holds everything else out of the water, while the drilling modules and crew quarters are located on the surface deck. Fixed platforms offer stability but no mobility, and today they're primarily used to tap moderately shallow, long-term oil deposits. They can drill about 1,500 feet below the surface, but they're costly to build, so they usually require a large oil discovery to justify their construction.
 
Jack-up rig: For smaller, shallower offshore oil deposits that don't warrant a permanent platform, or for drilling exploratory wells, oil companies may use what's called a "jack-up rig." The rig's floating platform is towed into position by barges, then lowers its support legs down to the sea floor, raising the rig above the water's surface. The platform can then be adjusted to varying heights along its tall legs, essentially using the same principle employed by a tire jack (hence the name). Jack-up rigs were traditionally used in shallow water because it wasn't practical to lower their legs to great depths, but newer models such as the Tarzan-class rigs are now stretching those limits. They're also considered safer than some other types of moveable rigs, such as drilling barges, since their surface facilities are elevated from the water and less susceptible to waves and weather.

Compliant tower: Compliant-tower rigs are similar to fixed platforms, since both are anchored to the seabed and hold most of their equipment above the surface. But compliant towers are taller and narrower, and unlike fixed platforms, they sway with the wind and water almost as if they were floating. This is possible because their jackets are broken into two or more sections, with the lower part serving as the base for the upper jacket and surface facilities. This lets compliant towers operate at greater depths than platform rigs, potentially up to 3,000 feet below the surface.
 
Floating production system: As oil companies expand into ever-deeper waters, they've had to embrace less traditional methods of getting oil up to the surface. This often means deepwater rigs are buoyant and semisubmersible, floating partly above the surface while pumping up oil from deep wells. Some use wire and rope to connect with a stabilizing anchor, while others — including the now-sunken Deepwater Horizon, pictured at right in June 2009 — are "dynamically positioned," using computer-coordinated thrusters to keep them in place. These floating production systems are used in water depths from 600 to 6,000 feet, and are among the most common types of offshore rigs found in the Gulf of Mexico. Since their wellheads are located on the sea floor rather than a surface platform, as on fixed-platform rigs, extra care must be taken to avoid leaks. A machine on deepwater wellheads known as a "blowout preventer" is supposed to prevent oil from escaping, but the Deepwater Horizon's blowout preventer failed after the rig sank.

Tension-leg platform: Another rig that can drill beyond a mile is the tension-leg platform, which consists of a floating surface structure held in place by taut, vertical tendons connected to the sea floor. And for drilling smaller deposits in narrower areas, an oil company may instead use a miniature version known as a "Seastar," which allows for relatively low-cost production of small deepwater oil reserves that would otherwise be uneconomical to drill. Seastar rigs can drill to depths from 600 to 3,500 feet, and are also sometimes used as satellite or early-production platforms for large deepwater discoveries.
 
Subsea system: Floating production systems, drillships and even some pre-existing platform rigs use subsea wellheads to extract oil directly at the seabed, siphoning the crude up through risers or pipes to the surface. A subsea drilling system includes a deepwater production module that rests on the sea floor (pictured at right while still on land), as well as any transportation lines that channel the oil to surface facilities. Those facilities may be aboard a nearby platform rig, a ship floating overhead, a centralized production hub or even a faraway onshore site, which makes subsea oil rigs versatile as well as nimble, offering oil companies several options for tapping otherwise hard-to-reach deposits. But as the Deepwater Horizon spill has shown, the inaccessibility of such deep oil wells also makes it difficult to fix leaks.

Spar platform: Named after the tall, vertical "spar" (aka mast) of a sailing ship, spar-platform rigs use a single, wide-diameter cylinder to support a surface deck from the sea floor. A typical spar platform in the Gulf of Mexico has a 130-foot-wide cylinder, and about 90 percent of its overall structure is hidden underwater. Spar cylinders are available at depths up to 3,000 feet, but existing technology can extend this to about 10,000 feet, making them one of the deepest-drilling types of offshore rigs in use.

Image credits
Jack-up rig: Library of Congress
Deepwater Horizon rig: ZUMA Press
Subsea production module: U.S. National Energy Technology Laboratory

Source : www.mnn.com