Summary: Remote Sensing

Read the summary and the most important questions on Remote Sensing

• 1 Introduction

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• What is the obvious source of elecotromagnetic energy that you can think of? What remote sensing device do you personally use to detect this energy?

  The most obvious source is the sun. The sun provides the inital energy source of much of the remote sensing of the Earth surface. Our eyes are the remote sensing device that we humans use to detect radiation from the sun

• The infrared portion of the electromagnetic spectrum has two parts: the reflective and the emissive. Can you take photographs in these wavelength ranges?

  No photographic films exist to directly record emissive infraread (heat).
  

  • If they did, then they would have to be cooled (and kept very cold during use), which would be very impractical. Otherwise the temperature of the camera would be recorded. However there are a number of electronic devices which detect and record thermal infrared images.

• What do you think would be some of the best atmospheric conditions for remote sensing in the visible portion of the spectrum?

  • Around noon: sun at its most directly overhead point, which would reduce the distance the radiation has to travel and therefore the effects of scattering to a minimum
  • Sunny day
  • Dry
  • No clouds: will ensure an uniform illumination and no shadows from clouds
  • No pollution: would minimize the scattering and absorption that would take place due to water droplets

• In the night it is possible to see the outline and very slight detail of the dark portion of the moon, where is the light coming from, that illuminates the dark side of the moon?

  The light originates from the sun, hits the earth, bounces up to the dark side of the moon and then comes back to the earth and into your eye

• Is there are passive equivalent to the radar sensor?

  Yes. The passive microwave radiometer does not carry an illumination source, relying instead on dectecting naturally emitted microwave energy. Such an instrument can be used for detecting, identifying and measuring marine oil slicks

• Should RS data also be geo-referenced?

  This is not necessary, could use an image as a reference and register all other data to this reference image

• If you want to map 2 different trees species in a mixed forest using remote sensing data, how would you do this?

  • Using the visible portion of the spectrum is not useful, because both the types will appeart as smiliar shades of green to the eye
    
  • Also, trying to distinguish the different types based on tree crown or size might be difficult 
  • Also, looking at the reflectance it is difficult 
  • THUS: near-infrared --> although they both reflect a significant portion of incident radiation --> black and white infrared film, around 0.8 wavelength would be ideal.

• What is important when using remote sensing in GIS?

  • The information layers match geometrically --> needs to be the same coordinate system
    
  • Well-considered combination of mutually reffering data sets of various kinds of position-bound thamtic data 

• What are infrared colours during the day and night?

  Day:
  

  • Blue = cold
  • Green --> yellow --> red = hot 
  • White = warmer

  
  Night:
  

  • Dark colours = low temperature
  • Bluish colours = quite high relative to the surrounding

• What is passive remote sensing?

  • RS using reflected solar raditation: in the visible infrared and neo infrared part of the spectrum which is most comparable to our human eyes
    
  • RS using emitted radiation by objects: the sun in heating the earth surface clearly above absolute 0 and as a result the surface is emitting radiation. But different objects emits different amounts of radiation. Vegetation under drought stress emits more radiation than well drained and well irrigated vegetation. We can measure that, it is still passive, but it is an important application for Remote Sensing