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Hemisphere Calibration

• Effects on calibration– Stray Light – Shield Starting with Crystal– Stable Supply and Selected bulbs - Crystal– Warm-up Time – Operational issue– Humidity – Improvement possible– Temperature– Optics Degradation

• Deployment Results– Crystal, Texas 2002, Thorpex

Ames Research CenterAmes Research Center Airborne Sensor FacilityAirborne Sensor Facility

-1.0%

-0.5%

0.0%

0.5%

1.0%

0 50 100 150 200 250

Minutes x 2

Perc

en

t ch

an

ge

Diode

Hemisphere Monitor Diode vs Run Time

• Varying warm-up time changes output by over 1%• Preflight data taken with 15 to 45 minutes of

warm-up• Loud alarm needs to signal when to take data

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Preflight Humidity sensitivity• Port 2 fogs often• N2 Purge needed• Fore optics occasionally

mist over slightly

Thorpex MAS Humidity Effects

-80%

-70%

-60%

-50%

-40%

-30%

-20%

-10%

0%

10%

0 5 10 15 20 25

channel #P

erce

nt C

hang

e

614 - 16.9C

615 - 17.3C

616 - 17.3C

617 - 16.3C

618 - 16.7C

619 - 16.6C

931 - 19.4C

932 - 20.5C

934 - 19.5C

935 - 18.9C

Texas 2002 MAS Preflight Change

-50%

-40%

-30%

-20%

-10%

0%

10%

0 5 10 15 20 25

Channel #

Pe

rce

nt

Ch

an

ge

fro

m S

tart 913

914

916

917

918

919

920

921

922

923

30" sphere

Ames Research CenterAmes Research Center Airborne Sensor FacilityAirborne Sensor Facility

Hemisphere Temperature Stability, Crystal, Texas 2002, Thorpex

Hemisphere Temperature StabilityData from Crystal, Texas 2002, Thorpex

Current changes 20ppm / C

-1.0%

-0.5%

0.0%

0.5%

1.0%

10 15 20 25 30 35

Degrees C

Per

cen

t ch

ang

e

Monitor Diode

Lamp Amps

Lamp Volts

These data points were taken at exactly 25 minutes after Hemisphere start

Ames Research CenterAmes Research Center Airborne Sensor FacilityAirborne Sensor Facility

CRYSTAL-Face: Daily Hemisphere Response & Projected Degradation Used in L-1B Calibration (based on 30” sphere)CRYSTAL-Face: Daily Hemisphere Response & Projected Degradation Used in L-1B Calibration (based on 30” sphere)

Ames Research CenterAmes Research Center Airborne Sensor FacilityAirborne Sensor Facility

THORPEX: Daily Hemisphere Response & Projected Degradation Used in L-1B Calibration (based on 30” sphere)THORPEX: Daily Hemisphere Response & Projected Degradation Used in L-1B Calibration (based on 30” sphere)

Ames Research CenterAmes Research Center Airborne Sensor FacilityAirborne Sensor Facility

Crystal Sphere vs Hemisphere & Humidity

Crystal Sphere vs Hemisphere Slopes & Humidity

-5%

-4%

-3%

-2%

-1%

0%

1%

2%

3%

4%

5%

948 949 950 951 952 953 954 955 956 957

flight #

De

lta

sp

he

re -

de

lta

he

mis

ph

ere

30

40

50

60

70

80

90

ch1

ch2

ch3

ch4

ch5

ch6

ch7

ch8

ch9

ch10

ch11

ch12

ch13

ch14

ch15

ch16

ch17

ch18

ch19

ch20

ch21

ch22

ch23

ch24

ch25

humidity

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Texas 2002 Port 1 Preflight Change

Thorpex Port 1 Preflight Change

-8%

-6%

-4%

-2%

0%

2%

4%

6%

1 3 5 7 9

channel #

Pe

rce

nt

Ch

an

ge

fro

m

Sta

rt

614 - 16.9C

615 - 17.3C

616 - 17.3C

617 - 16.3C

618 - 16.7C

619 - 16.6C

931 - 19.4C

932 - 20.5C

934 - 19.5C

935 - 18.9C

30 inch

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• Used by Keck Telescope

• Started in Hawaii ’03• Eliminated

degradation• Cleaned after

every flight

CO2 Snow Cleaning