:: On Remote Sensing ::

FAQ on Satellite Remote Sensing

What purpose are satellite images used for?

What is better space imaging or aerial survey?

From which satellites can images be purchased?

How to choose an image?

What can be found in satellite image?

What does Spatial Resolution of image mean?

What does Panchromatic or Multispectral Image mean?

What does Radiometric Resolution mean?

How can be known if there are any archived images of area of interest?

How to order satellite image?

What imagery format will be delivered?

Was there any kind of processing of images to be delivered?

What is a minimum area to order?

What is Scene and is it possible to order an optional-formed scene?

How many days after placing the order the archived image may by delivered?

Is it possible to order new imagery of required area in case there no proper archived data?

What is the height accuracy of DTM based on multi-satellite processed stereo images?

What is the frequency of satellite pass over the same point on the earths surface?

At what time does satellite pass over Moscow?

Where one can get the details of satellite characteristics?

What is Orthorectification of image?

What purpose are space images used for?
Space images are widely used in various fields of human activity such as natural resources study, natural disaster monitoring and impact assessment, mans impact study, construction, design-survey works, urban and land cadastre, planning and management of territory development, urban planning, geology and mineral resources development, industry, agriculture and forestry, tourism etc. The state-of-the-art geoinformation technologies and generating maps of different scales are unfeasible without using space images.

What is better space imaging or aerial survey?
Satellite image and aerial photo compare their merits and demerits:

Optical satellite image

Aerial photograph (on film)

The price increases proportionally to space extension

The price less increases with space extension  

Data is recorded in digital form so there is no need for film processing.

Data is usually delivered in taped form, so it is needed to scan and correct imagery for flight direction.

Cloudiness is an insuperable obstacle for surface surveying. The revisit period can be more than 3 days

Aircraft is capable of surveying under the clouds and can repeat it next day

Minimum order area is only 64 sq km

Aerial survey of small areas is unprofitable

No authorization is needed for satellite imaging

There are complicated and long processes for planning, authorization and adjustment of aerial surveying

A spatial resolution of 50cm is considered to be the best nowadays

Images with the resolution of up to several centimeters depending on flight altitude may be taken

Visible and IR images are acquired simultaneously

Imagery from tape recordings is derived separate in color and infrared modes

One scene covers urban construction of 10km?10km or 16km?16km in area (IK and QB)

Picture size is 3.6?6.4 km for 1:40000 scale imagery with 1m pixel resolution

Mosaic generation takes less time

Mosaic generation takes more time

Preferred surveying direction is North-South than West-East because of popularity of near-polar satellite orbits

Surveying direction is of no importance

Average time of image delivery is 7 days from the date of ordering. The time can be extended to one month for cloudy and rainy areas

The time of image delivery  depends on the availability of aircraft and flight weather only

Fast and easy processing of digital data under office conditions

Labor-intensive and costly processing of aerial photos under office conditions

The possibility of covering vast regions by one image with no need for further mosaicking some segments

The mosaicking of small tiles into one whole image massive is required

From which satellites can images be purchased nowadays?
The RESURS-DK1 images.  Both archived images and images from in-orbit satellites are available.

 

How to choose an image?
The best way is to contact our specialists who will help you to analyze your request and give essential recommendations. You may call +7 (495) 925-04-19, 229-43-89, or send e-mail to ntsomz@ntsomz.ru or fill in a form.

 

What can be found in satellite image?
Depending on spatial resolution, the objects comparable with the value of unit resolution cell (pixel) may be distinguished in satellite image. Nowadays 50cm is considered to be the best spatial resolution.

 

What does „Spatial Resolution“ of image mean?
Spatial resolution is a value which characterizes the size of smallest objects seen in a picture.

 

What do „Panchromatic“ or „Multispectral“ images mean?
Panchromatic images cover essentially the most region of the electromagnetic spectrum range (450-900nm) therefore they are black and white.

Multispectral (or spectrozonal) images are presented as independent spectral bands (RGB and Infrared bands) or as different band combination for acquiring color imagery. Alternative synthesis of different bands enables solving numerous thematic tasks and helps to interpret images as well.

 

What does „Radiometric Resolution“ mean?
Radiometric resolution capability is determined by the number of color gradations corresponding to transition from brightness of the black body to that of the white body and expressed in terms of bits per pixel. Therefore in case of radiometric resolution of 6 bits per pixel we have 64 color gradations (2(6) =64), of 8 bits per pixel 256 gradations (2(8) =64), of 11 bits per pixel 2048 gradations (2(11) =2048). Presently, satellite sensors usually have 8bit resolution, but there are some sensors having better radiometric resolution what allows detecting more details in very dark or very light areas of image (e.g. 11bit resolution for WorldView-1, IKONOS, QuickBird, OrbView-3 and 16bit resolution for EO-1)

 

How can be known if there are any archived images of an area of interest?
To this end you need to email: ntsomz@ntsomz.ru or by Tel: +7 (495) 925-04-19, 229-43-89 with references to interested area and spatial resolution. You may send geographic coordinates of requested region, map fragment with delineated area just describe the required area (e.g. within the boundaries of Tver Region or Kolomna City).

 

How to order satellite image?
For ordering an archived image or new imagery data you should send email by: ntsomz@ntsomz.ru or by Tel: +7 (495) 925-04-19, 229-43-89 or to fill in a special application with references to interested area and spatial resolution. The best way is to send accurate geographic coordinates of requested region or vector files (Microstation, ENVI, ESRI, MapInfo).

 

What imagery format will be delivered?
You will receive geo-located images (1:100,000 scale for high resolution) in GeoTIFF format. On default images are delivered in WGS-84 reference frame and UTM projection. Images in other projections and coordinate systems may be also delivered100 000) â ôîðìàòå GeoTIFF.

 

Was there any kind of processing of images to be delivered?

Delivered images undergo geometric and radiometric correction (reception path-induced noises are eliminated).

 

What is a minimum area to order?

It depends on the requested images. For some satellites a minimal area to be ordered is given below:

 

What is scene and is it possible to ask for optional formed scene?

Scene is a part of dataflow received by satellite. The schemes of dataflow cutting into scenes differ for various satellites. One may order a free-form scene in case of high resolution data. Limitations are as follow: for extended objects the swath width should not exceed 5km, the distance between the polygons vertexes should be no less than 5km also. The number of polygon vertexes should not exceed 50.

 

How many days after placing the order the archived image may be delivered?
You may receive the archived image maximum in a week after receiving money on account.

 

Is it possible to order a new imagery of required area if there are no proper archived data?

Yes, sure. You may order a new acquisition (including stereo-pairs) almost from every satellite.

 

What is the height accuracy of DTM based on multi-satellite processed stereo images?
The accuracy of Digital Terrain Modeling (DTM) is 2-3m for IKONOS and QUICKBIRD and 8-12m for SPOT.

 

 

 

What is the frequency of satellite pass over the same point on the earths surface?
The frequency of satellite pass over the same point on the earths surface is called revisit time. Different satellites have different revisit time.

 

At what time does satellite pass over Moscow?
Usually remote satellites have the sun-synchronous orbit and pass over the same point of the globe at the same time whatever the latitude. For example IKONOS and QuickBird satellites pass over the same point at 10.30 AM, be it Moscow or Krasnoyarsk.

 

Where one can get the details of satellite characteristics?
You can find the details on our site in Remote Sensing Facilities page or contact our specialists by Tel: +7 (495) 925-04-19, 229-43-89.

 

What is „Orthorectification“?
Orthorectification is a geometric correction of image wherein some corrections for considerable geometric distortions caused by the topography, camera geometry, and sensor errors are made. The orthorectification gives a planimetric accurate image. The most users carry out the orthorectification of satellite images since the tasks based on these images require a high accuracy positioning or indiscrete scale of a whole image. For instant, the orthorectification enables the following:

  • Image-based measurement;
  • Exact locating of some image details;
  • Obtaining data for GIS;
  • Combining an image with other image underwent the same orthorectification for more sophisticated research.


URL : http://www.ntsomz.ru/dzz_info/faq_dzz
Copyright ©