11/17/2014

1

Microwave Sensing: 1mm to 1 metre (mostly 1cm-30cm)

http://www.whrc.org/education/rwanda/pdf/Walker_SAR_Veg_Mapping.pdf

Microwave energy – unaffected by the atmosphere – 100% transmittance

11/17/2014

2

There is limited natural energy in microwave wavelengths … so pixel size needs to be large

Passive microwave sensing is a continuation of recording thermal energy in the microwave wavelengths. The signal is a brightness temperature but there is less terrestrial energy to sense, so a large pixel, ca. 10-25km is needed for radiometric resolution. Radiance = temperature x emissivity Remote sensing at microwave wavelengths is effective because … the relatively insignificant atmospheric attenuation for many microwave windows

= unaffected by clouds

Thermal sensors: AVHRR POES GOES ATSR MODIS

Microwave sensors: SMMR TMI-TRMM AMSR SSM/I ESMR

11/17/2014

3

http://members.home.nl/wim.h.bakker/pm.html

Partial list of passive microwave sensors (1998)

Sea Surface Temperature (Maurer) a. Thermal IR, b. Microwave passive

Thermal IR: higher resolution and accuracy;

Microwave: unaffected by clouds, but sensitive to precipitation and surface roughness

11/17/2014

4

http://www.ssmi.com/sst/sst_data_daily.html?sat=tmi_amsre

http://www.ssmi.com/ssmi/ssmi_data_weekly.html

11/17/2014

5

http://cics.umd.edu/~rferraro/SSMI_Climate.html

The SSM/I is a seven channel passive microwave radiometer operating at four frequencies

(19,35, 22,235, 37, and 85.5 GHz)

http://www.ccin.ca/CMS%20FTP%20Data/snow/swe/snow_swe.html Most Recent Snow Water Equivalent Map for Canadian Prairies

11/17/2014

6

http://www.ssmi.com/

11/17/2014

7

Changes in snowmelt, Greenland

11/17/2014

8

So far, we have looked only at 'passive' remote sensing systems. These passively record reflected or emitted electromagnetic energy.

As passive microwave sensors deal with very low resolution, more applications in these wavelengths use active sensors:

RADAR

Passive Active

RADAR is the most commonly used space-based active sensing system.

It is an acronym for RAdio Detection And Ranging.

The signal is reflected back to the transmitter when it detects an object;

The time taken yields the distance;

http://www.nrcan.gc.ca/earth-sciences/geography-boundary/remote-sensing/fundamentals/2021

11/17/2014

9

Plan position indicators (PPI) produce a type of image. These radars use a circular display screen to indicate objects surrounding the rotating antenna. They are commonly used for weather monitoring, air traffic control and navigational systems.

Radar systems were first implemented in the 1930s to detect ships on water and to measure their proximity, and later airplanes.

Imaging radar systems have been in use since the 1950s.

The original technology was developed during WWII: early german radar.

Non-imaging radar

UNBC bird study using RADAR – near Chetwynd

(Dr. Ken Otter)

Dokie Ridge

Site of wind turbines

11/17/2014

10

RAdio Detection And Ranging: The RADAR device transmits energy, a portion of which is returned to the sensor. The time taken gives the distance (location) of the target, the strength of the return describes its characteristics.

Satellite imaging radar started with SEASAT ,

launched in 1978. http://fas.org/irp/imint/docs/rst/Sect8/Sect8_6.html

As it is not affected by darkness or weather, it is especially useful in arctic regions for mapping ice; and tropical areas, which are consistently cloud covered as well as other areas often cloud covered, both temperate and tropical.

Ireland, 1991: Radar and Visible image

11/17/2014

11

Most early imaging RADAR was airborne, e.g. Calgary Intera technologies: Panama

In the microwave, it is more usual to refer to bands by frequency in Gigahertz (waves/second) than by wavelength, especially for RADAR 1cm to 10cm = 30 to 3 GHz

11/17/2014

12

multiband (multifrequency) image of San Francisco, CA,

SIR-A in November, 1981. The color scene is a Landsat subimage of the Selma Sand Sheet in the Sahara Desert within northwestern Sudan.

Because dry sand has a low dielectric constant, long P radar waves penetrate these small particles by several metres

11/17/2014

13

Vancouver, RADARSAT 2

Bright = higher texture Low = low dielectric constant ( / texture) Highest – corner reflectors

Radar image interpretation: Digital Numbers The response to radar energy by the target depends on three factors: Surface structure and roughness

Moisture content: electrical properties (dielectric constant)

Radar - surface geometry relationship

http://www.geog.ucsb.edu/~jeff/115a/remote_sensing/radar/radarroughness.jpg

11/17/2014

14

Foreshortening The hill slopes AB and BC are equal, but the foreslope (AB) is compressed (A'B') more than the backslope (BC) (B'C'), due to the radar imaging geometry.

Layover

The radar-facing slope (AB) will be imaged (B'A') as leaning toward the radar. This is due to the mountain top (B) having been imaged before the

base(A) due to RA > RB.

Radar - surface geometry relationship

http://hosting.soonet.ca/eliris/remotesensing/bl130lec13.html

Radar - surface geometry

relationship: shadows

11/17/2014

15

Selected RADAR satellite systems (Date launched, Wavelength, Resolution)

RADARSAT 2 (Canada) 2007 C 3-100m

Radarsat 1: launched in 1995, resolution 10-100m

Radarsat 2: launched in 2007, resolution 3-100m

11/17/2014

16

http://ice-glaces.ec.gc.ca/App/WsvPageDsp.cfm?ID=1&Lang=eng

11/17/2014

17

http://ice-glaces.ec.gc.ca/App/WsvPageDsp.cfm?ID=1&Lang=eng

Oceanography – oil spills

http://www.mms.gov/tarprojectcategories/remote.htm

http://earth.esa.int/ew/oil_slicks/wales_gb_96/

11/17/2014

18

http://www.ssmi.com/qscat/seawinds_data_weekly.html

DEMs from RADAR e.g. Shuttle Radar Topographic Mission, 2000

11/17/2014

19

TanDEM-X and TerraSAR-X (2010) High resolution Global DEM by 2014 – 10 m pixels

Ground penetrating radar (GPR) is a tool for analysing underground objects (such as graves), gravel and sand layers, and other underground structures. wavelengths: 20-70 cm

11/17/2014

20

Ground penetrating radar ice thickness measurements of Dokriani bamak (glacier), Garhwal HimalayaJ. T. Gergan, D. P. Dobhal and Rambir Kaushik (1998) Ice thickness measurements of Dokriani bamak (glacier) were carried out with a ground penetrating radar (GPR) pulse EKKO IV Sensor Software, Canada. The glacier ice thickness measured by GPR ranged from 15 m to 120 m. The computed total volume of glacier ice was 283.6 × 106 m3.

http://www.space.com/22598-greenland-s-grand-canyon-revealed-by-ice-penetrating-radar-video.html

Ice penetrating radar: http://www.ig.utexas.edu/research/projects/mars/education/ice_pen_rad.htm