Methods Used For the 2006 Radiance Lights The NGDC Earth Observation - - PowerPoint PPT Presentation

Methods Used For the 2006 Radiance Lights

The NGDC Earth Observation Group (EOG) Daniel Ziskin Kim Baugh Feng Chi Hsu* Tilottama Ghosh Chris Elvidge

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*Department of Materials Engineering, University of Tokyo.

The Observations

• The Defense Meteorological Satellite Program (DMSP) has

flown a long series of satellites.

• These satellites have an instrument called the Operational

Linescan System (OLS), which was designed as a cloud imager.

• Anthropogenic lighting is also detectable at night.
• The global data is the result of 5 by 5 pixel averaging

(smoothing) onboard.

• Digital OLS data have been archived at the National

Geophysical Data Center (NGDC) from 1992.

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The Sensor Normally Saturates Over Bright Urban Areas

• The sensor is operated for the purpose of

cloud detection.

• Six‐bit quantization (0 ‐ 63) and limited

dynamic range result in saturation over bright urban cores.

3 10 20 30 40 50 60 70

106.55 106.67 106.80

AVG VIS

Longitude at 10.8N

The Lights Ho Chi Minh City Saturate the Sensor

Pre‐Flight Calibration

• The saturation is a

function of Gain.

• The function is

read from a pre‐ launch test chart.

• The multipliers

are our way of normalizing DN values for intercomparison.

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Variable Gain

• Gain is adjusted continuously both

along the satellite track and along the scan line.

• The goal is to create “near

constant contrast” images for visual interpretation of cloud cover.

• Gains are not recorded in the data

stream.

• Gain is increased as the moonlight

decreases and stays low during the period of no moonlight.

• Gain is decreased as the moonlight

returns.

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2006 Fixed Gain Observations

• Clouds cannot be detected in the visible band nighttime

data when there is no moonlight.

• On these nights AFWA is amenable to having the gain

manipulated.

• During 2006 data were collected at low, medium and

high gain settings (15, 35, and 55 dB) on 24 hour increments.

• Gain 15 ‐ unsaturated observation of bright urban cores.
• Gain 35 – saturation possible in urban cores with

detection of urban edges and smaller towns.

• Gain 55 ‐ detection of dim lighting from small towns and

rural areas.

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Fixed Gain Data Along a Transect Crossing HCMC, Vietnam

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FIXED GAIN MULTIPLIER 15 100 35 10 55 1

100 200 300 400 500 600 700 800 900

106.55 106.67 106.80

AVG VIS

Longitude at 10.8N

Fixed Gain 15, 35, 55 of Ho Chi Minh City

Gain 15 Gain 35 Gain 55

Merging Fixed Gain Data

• Weighted Mean

– Number of observations – Proximity to saturation

• Smooth data may include saturated

pixels

8 100 200 300 400 500 600 700 800 900

106.55 106.67 106.80

AVG VIS

Longitude at 10.8N

Stable Lights and Fixed Gain 15, 35 of Ho Chi Minh City AVG VIS 15 AVG VIS 35 CALC MERGE

Blending with Stable Lights Product

• Fixed Gain products tend to

have three flaws:

– Low numbers of coverage in some places. – Anomalous events, such as fires, are included. – Noise.

• Blending with Stable Lights

processed from operational data improves each of these issues.

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Sao Paulo, Brazil F16 2006 RED – FG MERGED – Fires. GREEN – Stable Lights.

The Blending of the Fixed Gain and Stable Lights is Based on Linear Regression of Gain 55 and Stable Lights in the Nile Delta

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Comparison of the Stable Lights and Radiance Lights

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Stable Lights of Ho Chi Minh City RED = 60 ‐ 63 DN Radiance Calibrated Lights of Ho Chi Minh City Central Core ~ 800 DN

Ongoing Effort on Radiance Lights

• Low, medium and high fixed gain data

were collected in 1996‐97, 1999, 2000, 2003, 2006 and an ongoing collection is being made in 2010.

• NGDC is attempting to process a

consistent series of radiance products.

• Major issue to be resolved is how to

intercalibrate the products from the various years.

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Download the Data

You can download the 2006 radiance product from:

www.ngdc.noaa.gov/dmsp/download_radcal.html

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