Lectures 3 Flashcards
XPGR
Cross-polarized gradient ratio
Developed by Waleed; other techniques also used
Combinging freq and polarization for amplified melt signal
Threshold allows classification of melt
ICESat
need stuff
GRACE
Gravity recovery and
can be used to measure ice balance
Mascon==
like a pixel, done by Luthcke
Assessing ice sheet contributions to sea level rise
Mass Balance = precipt - surface alblation - discharge
- Flux Method= assess net different between mass input and mass output from observations and models of each component
Mass Balance = precept (ice cores and models) - surface ablation (models) - discharge (InSAR and others)
Snow measurement (RS)
MODIS monthly snow over with fractional snow…….
Spectral albedo
differs for different surfaces–can be used to ID
NDSI
Normalized Difference Snow Index, uses bands from Landsat ™ and MODIS. Measuring in dark forests is hard, particularly in the tropics. Sensitive to small changes in NSDI or NDVI,,,,
NDVI
define
SWE
Snow water equivalent–mount of water that comes from an icepack. Use 19 and 37 GHz. When no snow, similar. When snow, brightness temp is different.
Important for fire modeling, flood forecasting, hydroelectric power, watershed management.
Classification techniques
GENERAL CONCEPTS:
- Each pixel has DN for each band
- N-D scatterpolots of DN by band form clusters (plot band 4 and band 5 on x, y). Closest in cluster has similar spectral signature.
- Each cluster has a mean distance from origin and angle. Together, these define the class vector.
- Other stats describe shape of cloud.
PDF–define
SUPERVISED (need knowledge of what’s there):
Used to cluster pixels in an image into particular ground cover types. Many supervised algorithms are available (Paralellepiped, minimum distance, etc)
1. user picks types / groups
2. select pixels from each class (called training class)
3. use training classes to estimate parameters of algorithm
4. Classify every pixel into type
5. Produce image / map
UNSUPERVISED (don’t have knowledge of what’s there):
Used to cluster pixels in data set based on stats only, without training classes. Two algorithms: Isodata and k-means.
Fast. Does not assume normally distributed PDF.
HYDROSPHERE LECTURE
HYDROSPHERE LECTURE
Hydrosphere applications (IMPORTANT)
list from slide–add instruments
- sea / lake surface temp–thermal, PM
- wind over lakes / ocean–AM, scatterometry
- chlorophyll–vis, NIR
- sediment–vis, NIR
- ocean circulation–TOPEX / POSEDISON, Jason, Metop, AM
- volume & mass change: Altimimetry (ICESat and aircraft, Gravity (GRACE)
- water extent–vis, NIR, AM
Cryosphere applications (IMPORTANT)
list from slide–add instruments
Water Cycle
see slide
Hydrological cycle
Global water cycle
three major pathways: precipitation, evaporation/transpiration and vapor transport
Total water radiance
surface, subsurfcae, volumetric, and bottom radiance
total (Lt) = Lp + Ls + Lv + Lb
Lp=unwanted path radiance (atmosphere)….etc
Why does water appear blue to our eyes?
Scattering in water column is important in the bviolet, dark blue, and light blue portions of spectrum (400-500 nm)..Nearly all NIR and MID is absorbed (for clear water)
Measuring surface extent of water
using active microwave (AM, e.g. Radarsat): surface roughness and moisture content affect reflection
- water will have specular reflection (dark)
- land will have diffuse reflection (some will return to sensor)
What about sediment?
- The spectral reflectance of sediment in surface water is function of quantity and characteristics (particle size, absorption, etc)
- Remote sensing must be validated in situ
- Can be done using a SECCHI DISK or spectroradiometer
Spectroradiometer
- measures radiation (in situ)
- used to collect spectral reflectance at a of pure water and water with various suspended segment and chlorophyll concentrations
- 252 bands between 368 and 1114 nm
Measurements using a Spectroradiometer
study this slide
Take away: 580-690 nm provides info….
Chlorophyll in water
Plankton: phyto, zoo, bacterio
- Phytoplankton is important for carbon fixation / CO2 sink. (Use CO2 in photosynthesis)
- Contain chlorophyll pigments that decrease blue and red reflectance, but increase green and NIR reflectance
- Different spectral response if mineral also suspended
Remote sensing of ocean color
color = life
Three main: CZCS, MODIS, SeaWIFS
Warmer the color (CZCS), the greater the chlorophyll concentration near the surface
Slide has details re platforms / spectral ranges
Sea Surface Temp
The temperature of the sea is the most important parameter in understanding the role of the ocean as a heat reservoir. SST is an important geophysical parameter, providing the boundary condition used in the estimation of heat flux at the air-sea interface. On the global scale this is important for climate modeling, study of the earth’s heat balance, and insight into atmospheric and oceanic circulation patterns and anomalies (such as El Niño)
SST types of sensors
SST can be derived from two types of satellite data, thermal infrared and passive microwave:
Thermal sensors
Sensors used for deriving SST include AVHRR, Along Track scanning Radiometer (ATSR), GOES, MODIS
good spatial resolution and accuracy
long heritage (over 30 years)
with thermal infrared (8-14 μm) the skin temperature (20 μm) at the sea-air interface can be measured
TIR measurements are affected by water vapor and clouds in the atmosphere, thus
atmospheric corrections are required
Sea Surface Temperature (SST)
Passive microwave sensors
PM sensors include SMMR, SSM/I, TMI, AMSR
clouds are transparent
long heritage (over 30 years)
relatively insensitive to atmospheric effects
lower spatial resolution and accuracy than with thermal, Due to lower signal strength of the Earth’s Planck radiation curve in the microwave region
sensitive to surface roughness (waves) and precipitation
measures SST at depth of 1 mm
Methods of TIR for SST
Three methods can be used:
* Split window: uses 2 channels (windows) that overlap in spectral sensitivity (formula coefficients differ day / night)
- Dual window: uses 2 channels that do not overlap
- Triple window: uses 3 channels
Oceanic Circulation importance
- Ocean is important as the atmosphere in transporting heat
- Mechanism is ocean currents
- Warm ocean currents transport warm water from the tropics northward where they release energy to the air
- Cold ocean currents transport cold water from higher latitudes toward the equator
Oceanic circulation, factors affecting
Winds Bottom topography Sea-surface height Sea-surface temperature Coriolis forces resulting from the rotation of the earth
Platforms for Oceanic Circulation–Sea Surface Height
The factor influencing the oceanic circulation determines the platform
Sea Surface Height
• Early platforms are Geosat and ERS-1 were designed for the remote estimation of sea-surface height
• NASA/CNES satellite TOPEX/POSEIDON, a sea- surface height sensor of high accuracy with an RMS error of 4.7 cm for TOPEX and 5.1 cm for POSEIDON
• Jason-1 (similar to TOPEX/POSEIDON)
Platforms for Oceanic Circulation–Ocean Winds
NASA scatterometer (NSCAT) produced data from Sept 1996 - June 1997 C-band 50 km grid resolution QuikSCAT SeaWinds scatterometer June 1999-November 2009 C-band 25 km spatial resolution for wind vectors measures winds of 3- 20 ms-1, with 2 ms-1 accuracy ERS1/2 scatterometer, Advanced scatterometer (ASCAT) METOP-A launched Oct. 2006 METOP-A launched Sept. 2012 METOP-C Planned 17
What sensors use for height?
Altimeters
How to measure wave direction and height
- Backscattered energy indicates surface roughness
- Orientation in imagery determines direction
ex: ERS-2 SAR
El Niño
Holy Child–always happens during x-mas
Unusual warming
extensive ocean warming in the equatorial eastern Pacific along the coast of Peru and Ecuador.
brings nutrient-poor tropical water southward along the west coast of South America in major events that recur at intervals of 3-7 years.
associated with atmospheric circulations having important consequences for weather and climate around the globe.
La Niña
unusually cold ocean temperatures in the Equatorial Pacific
El Niño and La Niña Impact on the Climate
At higher latitudes, El Niño and La Niña are among a number of factors that influence climate
- most clearly seen in wintertime
- El Niño :
warmer winter in the North Central States
cooler in the Southeast and the Southwest - La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in
the Northwest
Passive Microwave Sensing of Rain
Over the ocean:
- Microwave emissivity of rain (liquid water) is about 0.9
- Emissivity of the ocean is much lower (0.5)
- Changes in emissivity (as seen by the measured brightness temperature) provide and estimate of surface rain rate
Over the land surface:
- Microwave scattering by frozen hydrometeors is used as a measure of rain rate
- Physical or empirical models relate the scattering signature to surface rain rates
Tropical Rainfall Measuring Mission
- Precipitation Radar (PR)
- TRMM Microwave Imager
(TMI) - Visible and Infrared Scanner (VIRS)
- Cloud and Earth Radiant Energy Sensor (CERES)
- Lightning Imaging Sensor (LIS)
Grace and the water cycle
Gravity Recovery and Climate Experiment
Lake water storage anomalies
Terrestrial water storage
BIOSPHERE
BIOSPHERE
Hyperion
Hyperspectral imager–more than 200 bands, with 10-nm bandwidth
Applications: Biosphere
- Physical basis
- Spectral refelctance
- Assessment of plant stress
- Vegetation classification
- Estimation of biomass
- Angular reflectance characteristics
- Vegetation indices
- Phenological cycles
- Multi-sensor, multi-resoltuion considerations
