12/28/2001 #1

LEO 2001 IN SITU DATA Profiling Optics and Water Return (POWR) Package

Joe Rhea and Gia Lamela

12/28/2001 #2

LEO 2001 IN SITU DATA Specifics of Data Collected July 22 Through August 2, 2001

1) Profiling Optics and Water Return (POWR) PackageInstrument What is measuredHistar Water Absorption and Attenuation at 103 wavelengthsac-9 unfiltered Water Absorption and Attenuation at 9 wavelengthsac-9 filtered CDOM Absorption at 9 wavelengthsHydroscat-6 Backscattering in 6 wavelengths WetStar Stimulated Fluorescence (460nm out / 695nm in)Seabird CTD Conductivity (Salinity), Temperature, DepthWater bottles 8 bottles, each 2.5 liters (total 20 liters of water)

2) Pad Absorption, including Ap, Ad, Aph, and Ag

3) Chlorophyll concentration derived from both Turner and HPLC

4) Above-water Rrs (350-850nm) - Collected when sky conditions permitted

5) Sun Photometer - Collected when sky conditions permitted

6) Total Suspended Sediments / Laser particle Counter

12/28/2001 #3

LEO 2001 IN SITU DATA Summary of Data Collected July 22 Through August 2, 2001

Item: Processed by: Count: Status:Optic Profiles Rhea/Lamela 55 In ProgressRrs J. Rhea 17 CompletedPad Absorption G. Lamela 23 CompletedTurner [Chl_a] G. Lamela 23 CompletedHPLC [Chl_a] C. Trees 19 CompletedSun Photometer W. Snyder 19 CompletedTSS/LPC M. Sydor > 21 In Progress

Total stations sampled: 32

12/28/2001 #4

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LEO 2001 IN SITU DATA Rrs Spectra Collected July 22 Through August 2, 2001

12/28/2001 #5

LEO 2001 IN SITU DATA Station Locations, July 22 Through August 2, 2001

12/28/2001 #6

LEO 2001 IN SITU DATA Station Locations for Selected Rrs Spectra

12/28/2001 #7

LEO 2001 IN SITU DATA Selected Rrs Spectra

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12/28/2001 #8

PHILLS-1 2001 LEO-15 Data Status

Curtiss O. Davis, Jeffrey Bowles & William SnyderCode 7212

Naval Research Laboratory

Washington, DC 20375

12/28/2001 #9

Data Summary

• Data Collected.– Data collected 7/22,, 7/23, 7/25, 7/27, 7/28, 7/31, 8/01 and 8/02/2001.– 7/23 & 7/25 1.8 meter in-shore survey.– 7/27 & 8/02 Hi-Resolution (0.8 m) in-shore survey.– 7/31 AVIRIS over-flight.– 8/01 Time series (with AVIRIS over-flight).– 7/22 & 7/28 Engineering flights with science capability.

• Status Summary.– Data display small (~ 1 pixel) spatial displacement from laboratory calibration.– Some (< 1% of total) data contain dropped bands.– Pre and Post deployment laboratory wavelength calibrations agree, but differ

slightly from flight data.– Derived reflectance has been compared twice with simultaneous ASD

observations and are in reasonable agreement.– However, water pixels located next to bright land features display a rising

reflectance at wavelengths greater than 0.7 microns. Likely cause is sensor internal light scattering.

– Reflectance below 0.7 microns appears to be minimally effected.– Latitude and longitude positional information available.

12/28/2001 #10

Code 7212 Web Site (rsd-www.nrl.navy.mil/7212).

• Quick-looks available on Code 7212 Web Site (rsd-www.nrl.navy.mil/7212).– JPEGS of each aircraft scan.

– PowerPoint and Excel files displaying/listing planned scan coordinates.

12/28/2001 #11

Small Spatial Calibration Shift Across the Array

• The top figure is an RGB calibrated image of the first 150 lines of Run15Seq03 taken during the morning of 7/31/2001.

• The bottom figure is the same scene but with the radiometric calibration coefficients file shifted by 1 spatial pixel.

Result of Using Original Calibration Coefficient File

Result of Shifting Original Calibration Coefficient File 1 Spatial Pixel

12/28/2001 #12

A small (1-2 nm) Wavelength Shift Across the Array

• The top figure is the oxygen line of vegetation spectra extracted from various samples across run15seq00 taken on 7/31/01 am. The detector was in low gain.

• The bottom figure is averaged spectra taken from the left, middle and right third of the same image.

• The change in line shape suggests that there is a small spectral shift across the detector array.

• The bin width for this data set is ~4.8 nanometers.

• The change in line shape suggests that the spectral shift is probably 1-2 nanometers.

• This amount agrees with more quantitative analysis using Tafkaa.

12/28/2001 #13

Pre and Post LEO-15 PHILLS1 Wavelength Calibrations AgreeBut Flight Wavelengths Are Shifted By A Small Amount

• 512 channel linear calibrations were derived for Pre (cal010711) and Post (cal010815) LEO-15 deployment using Spec_Cal_Peak_Find1.pro.

• The wavelength calibrations for the 512 bands were then “collapsed” to produce 128 band wavelengths using Bin_Wav_Band.pro.

• The wavelengths shown above are the bin center wavelengths derived for the 128 bands.

• Agreement between the two calibrations appears to be within 0.33 nanometers.• This difference is much smaller than the wavelength offsets derived for

cal010711 using Tafkaa to obtain the best goodness of fit about selected atmospheric absorption lines for Run15Seq03 on 7/31/01.

Band # cal010711 cal010815 Diff Tafkaa Offsetmicron micron nm nm

10 0.427131 0.426798 0.333 1.2128 0.514701 0.514426 0.275 2.2179 0.762816 0.762705 0.111 2.6691 0.821196 0.821123 0.073 2.69115 0.937957 0.937961 -0.004 3.24

12/28/2001 #14

Spectral Stray Light Correction Required

• Scene averaged calibrated spectrum of water image. The different curves represents a prob512 of 0.0 (black), 1.0 (green) and 1.6 (red) x 10-4 of spectral stray light. Note that the radiance goes negative for 1.6 x 10-4 (the value used to correct last years images).

12/28/2001 #15

Data Calibration Procedure

• The PHILLS-1 calibration coefficients file has been derived using pre-LEO-15 laboratory calibration data.

• Observed counts are corrected for spectral stray light using a delta function scattering approximation with prob512 = 0.96 x 10-4.

• 128 spectral band data summed to 64 spectral bands to reduce small band to band calibration systematic effects.

• Radiometric calibration coefficients were computed using sample averaged laboratory wavelength calibration values.

• Resultant calibration coefficient file was then linearly “stretched” to match wavelength shifts computed by Tafkaa for flight data and then spatially shifted by 1 pixel.

• It is this stretched and shifted laboratory calibration coefficient file that is applied to the spectral stray light corrected flight data to produce the radiance data.

12/28/2001 #16

Line (Frame) Banding Example (010722 Run05seq05)

• Streaks are evident in the data, which for PHILLS-1 are most evident in spectral band 128.

• Inspection of these streaks indicates that they are properly placed spatially, but are spectrally shifted by one band.

• Inspection of one flight line with 8129 frames indicates that 64 lines are so shifted.

• If this is representative of the rest of the data, this indicates that 64/8129 lines or less than 1% of the data have this problem.

• A bad lines mask, identifying the bad lines, will be distributed with each data cube.

12/28/2001 #17

Sun Photometer Data are Available for Atmospheric Correction

• Data are available at 0.440, 0.675, 0.870, 0.936 And 1.020 Microns.

• A power law is fit to the data to obtain optical depth at 550 nm.

– Data above 0.9 microns are excluded.

R/V Northstar Sun Photometer 7/31/2001 15:01 - 15:39 GMT

y = 0.0552x-1.7081

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12/28/2001 #18

Sun Photometer Data Summary

Sun Photometer Summary

Date GMT (550 nm)Exponent H2O (cm-2)PhotometerLat_Deg Lat_Min Long_DegLong_Min Station7/23/2001 19:46-20:36 0.184 -1.677 2.4 Cal Panel 39 31.074 74 20.235 Cal

17:51-20:07 0.113 -0.778 1.7 R/V Northstar 39 28.3987 74 8.4116 PM5-E7/25/2001 13:59-14:01 1.013 -0.597 4.1 R/V Northstar 39 25.2385 74 18.0101 AM4-A7/27/2001 20:08-20:16 0.173 -0.365 1.1 Cal Panel 39 31.074 74 20.235 Cal

20:12-20:29 0.084 0.561 0.8 R/V Northstar 39 31.0825 74 20.1173 FISH-A7/31/2001 14:00-14:30 0.122 -1.919 1.8 Cal Panel 39 31.074 74 20.235 Cal

14:01-14:39 0.153 -1.708 1.9 R/V Northstar 39 31.0762 74 20.1035 FISH-A8/1/2001 15:16 0.177 -1.654 2.0 R/V Northstar 39 30.8624 74 14.7774 01-B

16:48 0.146 -2.233 1.8 R/V Northstar 39 31.5163 74 10.9934 02-A17:56 0.152 -1.766 1.8 R/V Northstar 39 34.8650 74 11.9610 03-A20:37 0.148 -1.666 1.5 R/V Northstar 39 27.5607 74 14.8117 04-A

8/2/2001 13:34 0.325 -2.170 2.2 R/V Northstar 39 27.4334 74 14.5871 01-A13:40-14:55 0.257 -2.035 1.9 Cal Panel 39 31.074 74 20.235 Cal

15:37 0.211 -2.069 1.8 R/V Northstar 39 23.9855 74 15.9401 02-A17:57 0.198 -1.681 1.6 R/V Northstar 39 26.1816 74 18.5462 03-A

Data on 7/31/2001 taken at same location.Cal Panel Photometer: #3129R/V Northstar Photometer: #3130

12/28/2001 #19

Great Bay Region Analysis (010731 Run15seq03)

• This image was collected at an altitude of 8500 feet.

• The sensor frame rate was 25 fps, data is binned into 64 spectral channels and the gain was low.

• The image is 1000 pixels wide and 1024 pixels long. The spatial resolution is 1.8 meters.

• The data has been calibrated using a calibration coefficients obtained with a laboratory plaque calibration setup corrected for spectral stray light.

• “X’s” mark the location of spectra shown on the following slides.

X(1)

X(2)

X(3)

X(4)

12/28/2001 #20

7/31/01 Run15seq03 Region #1, #2 Reflectance

• The single pixel Rrs derived from region #1 (S:551,L:985) and region #2 (S:956,L:708) of the PHILLS1 image shown previously. Also shown (as a blue line) is the smoothed ASD spectrum measured simultaneously from the R/V Northstar located near region #1. A mid-latitude summer atmospheric model has been assumed with marine aerosol ( = 0.12), relative humidity of 70% and 2 m/s wind speed. Water vapor was determined on a pixel by pixel basis.

• Agreement between ASD and aircraft derived reflectance is fair to good in the 0.4-0.7 micron range. However, an excess reflectance is apparent at longer wavelengths for region #1.

12/28/2001 #21

7/31/01 Run15seq03 Region #3, #4 Remote Sensing Reflectance

• The single pixel Rrs for two other regions in the image are shown. Region #3 was taken from [S:748,L:262] and region #4 from [S:488,L:838].

• Also shown (in blue) for comparison is the ASD reflectance derived for Region #1.• The Region #3 spectrum shows the effect of viewing the bottom through shallow

water.• The region #4 spectrum is for a land pixel and shows the characteristic red edge

rise in reflectance caused by plant material.

12/28/2001 #22

010731 Run15seq03 (996 nm)

• This image shows the relative reflectance at 996 nanometers. An equalization stretch has been applied to the image.

• Note the “glow” around the land features. It is in these regions that the rise in near-IR reflectance is most pronounced.

• This glow might be caused by atmospheric scattering or stray light entering the detector from inside, or possibly outside, the instantaneous FOV defined by the spectrometer slit.

• Note that the ASD measurement #1 shown previously occurred in a region with no land (that is, bright) features within the IFOV.X(1)

12/28/2001 #23

Latitude and Longitude Information

• Latitude and longitude information can be derived for each pixel in a scene based on in-flight C-MIGITS data and derived detector offset information.

• Comparison of known and computed positions of manmade features observed with low altitude data taken on 8/01/2001 were used to derive the sensor offsets.

• These sensor offsets were then used to derive “time offsets” for each of the other flights. Reasonable (5-10 pixel) RMS positional errors were obtained.

• It is therefore possible to produce latitude and longitude information for each scene based on the time offsets derived for each flight and the single set of sensor offset parameters. Positional errors are expected to be on the order of 10 meters or less for normal flight altitude data.

• This positional information will be stored in IGM files that will accompany any image that we provide and can be used in ENVI to georectify an image as desired.

12/28/2001 #24

Image Georectification Example

• IGM files will accompany any image that we provide and can be used to georectify an image as desired. An challenging example is shown above.

• It will probably be necessary to “rubber sheet” any georectified image to other ground truth information if spatial accuracy < 10 meters is desired.

Original Image Georectified Image

12/28/2001 #25

Products

• For each image sequence requested, the following products will be provided.

– Radiance and/or Remote Sensing Reflectance (Rrs) data cube.

– Band lines mask.

– Positional (IGM) file for that data cube.

– A land mask file will also be produced if an Rrs file is produced.

• We prefer to download data to the user’s FTP site. It may be possible for a user to download data from our site but NRL security requirements will need to be met.

• We can make CDs of SMALL data sets.

• Products will be produced with the best available information available at the time but will require user feedback to help identify, quantify and remove any remaining or newly discovered systematic effects.