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From Flashcardlet > Snow Survey Study Cards > Flashcards

Snow Survey Study Cards Flashcards

1
Q

What does NOHRSC stand for?

A

National Operational Hydrologic Remote Sensing Center

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2
Q

What are the typical dimensions of the flight lines?

A

10 nm long 1000ft wide area 2-3 sq miles

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3
Q

What is the product of the aerial survey?

A

Mean aerial soil moisture equivalent measurements which provide a representative sample of the survey area

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4
Q

What happens with the data?

A

Raw data is checked for accuracy by NOHRSC entered into SHEF and set to the NCRFC (River forecasting center)

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5
Q

Approximately how many flight lines are there?

A

2475 lines in 25 of the northern most states plus 7 Canadian Provinces

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6
Q

How are the lines determined?

A

Areas in the northern areas of the country and mountainous regions where significant snow is expected

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7
Q

What time of year is the snow survey/soil moisture conducted?

A

Year round

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8
Q

What becomes of the survey data?

A

The data is used to generate River and flood forecasts water supply forecasts and spring flow outlooks

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9
Q

What are sources of gamma radiation?

A

Gamma decay of naturally occurring radioisotopes and atmospheric interactions with cosmic ray particles

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10
Q

What are the principle contributors to the Terrestrial Gamma Radiation?

A

Potassium Uranium and Thorium

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11
Q

What other sources are detected by Rad Assist?

A

Airbourne Radon daughters cosmic rays and the radioactivity within the aircraft structure.

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12
Q

How are other gamma emittors flitered out?

A

The calibration process removes these additional contributors to isolate gamma associated with the Snow Water Equivalent

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13
Q

Where in the soil is the gamma radiation emitted from?

A

The upper 8 inches of the soil containing the Pot Ur and Thor

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14
Q

What is a gamma ray?

A

High energy high frequency electromagnetic emmision between x-ray and cosmic ray frequencies

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15
Q

How is the gamma radiation effected by the soil moisture?

A

Water attenuates the terrestrial radiation signal. The SWE is determined by comparing the snow covered data with the radiation attenuation over bare ground. Therefore SWE is measured from the attenuationi of the radiation signal solely from water mass.

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16
Q

What are cosmic rays?

A

Energetically charged subatomic particles(protons, helium and electrons (1%)) originating in outer space.

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17
Q

What is the purpose of the cosmic flight lines?

A

To isolate purely the aircraft and cosmic contributions to the gamma spectrum and remove them from the SWE equation

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18
Q

How are cosmic flights flown?

A

At high altitudes (to reduce terrestrial interferance) lines separated by at least 3000ft flown over lakes where radon concentrations are low

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19
Q

How does radon affect the system?

A

Radon alters the Uranium readings causing errors in the data

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20
Q

Why would crystal attenuation be lost at high altitudes?

A

The low concentration of particles is so low that the crystals stop working

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21
Q

What exactly is the crystal?

A

Sodium Iodine salt

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22
Q

How does the NaI detect gamma?

A

When activated with thallium and subjected to ionized radiation emits photons which is detected by scientillation (light to voltage) material

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23
Q

Why must be crystals be contained in a hermetically sealed assembly?

A

NaI is hydroscopic

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24
Q

What is the name of the Gamma detector onboard?

A

Radiation Solutions RSX-5

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25
Q

How many crystals are in the RSX-5?

A

4 downward facing and 1 upward facing

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26
Q

What are the temperature limitations of the crystals?

A

ā€œ-30C to +45Cā€ however avoid rapid temperature shocks

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27
Q

What is the first sequence of events for gamma detection?

A
  1. Crystals convert gamma to light
28
Q

What is the second sequence of events for gamma detection?

A
  1. photomultiplier converts to electrical signal
29
Q

What is the third sequence of events for gamma detection?

A
  1. digitally analyzied by Advanced Digital Spectrometer (ADS)
30
Q

What is the fourth sequence of events for gamma detection?

A
  1. Rad-Assist monitors data real-time
31
Q

What is the fifth sequence of events for gamma detection?

A
  1. Counts are then fed to the Airboarne Gamma Data Acquisition Software (AGDAS) to determine SWE/Soil Moisture/background data
32
Q

What atmospheric conditions must be factored into the SWE equation?

A

Distance from the ground (source) Temperature Pressure

33
Q

Why must the atmospheric conditions be used in the SWE equation?

A

Density of the air mass can cause an error of 0.95cm

34
Q

What three atmospheric sensors must be operational for snow survey?

A

Radar altimeter Temperature sensor Pressure sensor

35
Q

Where does the RSX-5 obtain temperature and pressure?

A

Through hard connections with the aircrafts Air Data Computer (ADC)

36
Q

What does one inch of mercury equate to in altitude?

A

1000ft

37
Q

What is the BG.dat file?

A

Contains the estimated back ground correction data for each line determined from previous surveys

38
Q

What is an important fall data check with regards to the BG.dat file?

A

The background data must contain expected conditions for every line at the time of future airbourne SWE for the coming winter

39
Q

What is required for each line to a successful survey?

A

A correct Mean Soil Moisture estimate for each line

40
Q

What is the first primary set contained in the BG.dat file?

A

Values for K Th and Gross Counts representing counts needed to calculate a normalized 25% SM value

41
Q

What is the second primary set contained in the BG.dat file?

A

List of values which reporesent and estimate of the soil moisture values for each line or an actual SM value if line has been flown (Date flown Rounded SM value Background data)

42
Q

Who requests the surveys?

A

River Forecasting Center and the Weather Forecasting Office requests surveys of river basins for hydrologic and forecast models

43
Q

How are is the data disemilated?

A

SWE values are provided to NWS in SHEF format and distributed via AWIPS to NOHRSC data assimilation program and incorporated into the NSA

44
Q

What is the first of the four general aspects of the Aerial Survey?

A

Radiation sensed from low flying aircraft

45
Q

What is the second of the four general aspects of the Aerial Survey?

A

Water mass attenuates the radiation signal

46
Q

What is the third of the four general aspects of the Aerial Survey?

A

The difference between the raw gamma values and the MSM equals the SWE

47
Q

What is the forth of the four general aspects of the Aerial Survey?

A

Measures attenuation of radiation signal due solely to the intervening water mass

48
Q

What is the first of the five limitations of the system?

A

Can determine up to 39 inches of water

49
Q

What is the second of the five limitations of the system?

A

Does not measure snow depth

50
Q

What is the third of the five limitations of the system?

A

Not sensitive to phase of water

51
Q

What is the fourth of the five limitations of the system?

A

Accounts for moisture in the atmosphere

52
Q

What is the fifth of the five limitations of the system?

A

Vegetation does not affect the readings

53
Q

What are the dimensions of the flight line coverage?

A

10 mi long, 100ft wide covering 2-3 sq mi

54
Q

What is the soil moisture estimate usually set at?

A

35%, which is the typical field holding capacity

55
Q

After both the soil moisture and SWE flights have been flown, how can inaccuracies be accounted for?

A

If the hydrologists believe the soil contains more moisture than orginal estimates (due to drought) then the amount of SWE calculated during the second flight would be reduced.

56
Q

What are three inaccuracies of the aerial survey?

A
  1. Systematically underestimate SWE values 2. Not representative of the overall area 3. 1000 ground samples are needed to get a good comparison with the aerial data.
57
Q

What is the weight of the cage assembly?

A

320lbs

58
Q

What does the DPU (Data Processing Unit) do?

A

Collects the raw data from the RSX-5 crystals, stores and processes the data for use by RadAssist.

59
Q

What is the purpose of RadAssist?

A

Displays currect status of the gamma spectrum, GPS health and tuning data from the DPU.

60
Q

What are the 3 DPU inputs?

A
  1. 28VDC 2. GPS (built-in but utilizes aircraft antenna 3. Pressure Altitude (air mass density) 4. Absolute Altitude (RadAlt for depth of air mass calculations) 5. Temperature (manually inputted through AGDAS)
61
Q

What does AGDAS stand for?

A

Airborne Gamma Data Acquisition System

62
Q

What is the purpose of the AGDAS?

A

Uses the data to calculte Snow Water Equivalent values.

63
Q

What is the purpose of the network switch?

A

Connects the DPU, AGDAS and the RadAssist Laptop.

64
Q

Why does the system require DC power?

A

For the radar altimeter.

65
Q

The GPS splitter provides antenna input to what devices?

A

the DPU and the Garmin 496.

66
Q

What is the temperature tolerance of the RSx-5?

A

ā€œ-30C to +45Cā€ however avoid rapid temperature shocks

From Flashcardlet (17 decks)

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