STRUCTURE: SLA02(MEGASTRUCTURE)

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TP STRUCT -> TIMEPArray[1]

RP STRUCT -> RANGEP Array[1]

BP STRUCT -> BOUNCP Array[1]

PAP STRUCT -> POSSATTP Array[1]

EP STRUCT -> ENGP Array[1]

WAVGRP STRUCT -> FWAV Array[1]

STRUCTURE:SLA02.TP (TIME PARAMETERS GROUP)

TAG NAME & DESCRIPTION

MES* Mission elapsed seconds computed with full corrections (in seconds)

LASTIME* Laser shot time tag (in seconds)

SHUT_DIFF* Difference of shuttle MES and LASTIME at minute pulse (in seconds)

MES_CORR* Functional fit of SHUT_DIFF (data edited) evaluated at LASTIME for every shot (in seconds)

MES = LASTIME + MES_CORR

STRUCTURE:SLA02.RP (RANGE PARAMETERS GROUP)

TAG NAME DESCRIPTION

RANGE_CORR* SLA range corrected for troposphere delay (assuming standard atmosphere) and SLA range bias (meters).

STRUCTURE:SLA02.BP (BOUNCE-POINT PARAMETERS GROUP)

TAG NAME & DESCRIPTION

LAT* Geodetic Latitude of geolocated shot bounce-point (in degrees North or South) in Topex/Poseidon (T/P) ellipsoid reference frame which is essentially identical to WGS-94 ellipsoid. Defined as the acute angle between the semi-major axis and the line through the observer perpendicular to the spheroid.

LON* Geodetic Longitude of geolocated shot bounce-point (in degrees East) in T/P ellipsoid reference frame, essentially identical to WGS-94 ellipsoid. Defined as the angle measured eastward in the equatorial plane between the Greenwich meridian and the observer’s meridian.

ELLIP_HT* Ellipsoid height of the geolocated shot bounce-point (in meters), perpendicular to the reference ellipsoid, in T/P ellipsoid reference frame, essentially identical to WGS-94 ellipsoid.

SURFACE_1* Ocean Surface Model (in meters); Ohio State University 95 (OSU95) Mean Sea Surface (MSS).

SURFACE_2* Time varying ocean surface correction (in meters); Ray Pathfinder Ocean Tide Model.

SURFACE_3* Smoothed residuals of SLA to Ocean Surface difference (in meters).

SURFACE_3 = SURFACE_1 + SURFACE_2 - ELLIP_HT (smoothed)

GEOID* Geoid undulation at shot bounce-point (NASA/NIMA Earth Geoid Model-96; EGM-96) (in meters).

ORTHO_HT* Orthometric Height (in meters). Includes SURFACE_3 correction (linearly extrapolated from ocean residuals)

ORTHO_HT = ELLIP_HT + SURFACE_3– GEOID

STRUCTURE:SLA02.PAP (POSITION AND ATTITUDE PARAMETERS GROUP)

TAG NAME & DESCRIPTION

SATHT* Ellipsoid satellite height (Center of Mass) (in meters) in T/P ellipsoid reference frame, essentially identical to WGS-94 ellipsoid.

ECFX_SHOT* Earth Centered Fixed X-coordinate of shot bounce point (in meters)

ECFY_SHOT* Earth Centered Fixed Y-coordinate of shot bounce point (in meters)

ECFZ_SHOT* Earth Centered Fixed Z-coordinate of shot bounce point (in meters)

AZIMUTH* Degrees from true North of laser vector (0 to 360 clockwise from North)

AOFFNADIR* Degrees from Nadir of laser vector (0 = Nadir, 90=Horizontal)

STRUCTURE:SLA02.EP (ENGINEERING PARAMETERS GROUP)

TAG NAME & DESCRIPTION

XMIT_EN* Transmit energy (counts, not calibrated)

RECEIVE_EN* Received energy on channels 1, 2, 3 (counts, not calibrated)

THRESH* Detection threshold level on channels 1, 2, 3. Array of 3 thresholds for the 3 differently filtered channels.

(counts, not calibrated)

CHANNEL* Which was the fastest channel triggered, defining which channel was used to measure the range.

Channel 1 = 16.6 MHz (intermediate filter)

Channel 2 = 5.8 MHz (slowest filter)

Channel 3 = 32 MHz (fastest filter)

Channel 4 ranging was disabled.

WAVE_OFFSET* Offset applied when reading from digitizer memory to ensure that the stop pulse, defined when the leading edge of the received signal exceeds the detection threshold, is contained within the stored waveform. A variable depending on which was the fastest channel triggered. (counts, not calibrated)

VGA* Variable Gain Attenuator setting for the detector sensitivity (Bytes). A measure of the DC voltage applied to the VGA.

VGA control Volts = VGA (bytes) * 20.0/1000.0

DIGI_ATTEN* Digitizer Attenuator Setting (dB).

SCALE_FACTOR* Waveform Amplitude Scale Factor (Unitless).

Waveform Amplitude Scale Factor = Detector Scale Factor (Unitless) * Digitizer Scale Factor (Unitless)

Digitizer Scale Factor = invlog [ DIGI_ATTEN (in dB) /(-20.0)] (Unitless)

Detector Scale Factor = invlog [Detector Attenuation (in dB) /(-20.0)] (Unitless)

Detector Attenuation (in dB) = (detector gain at VGA control voltage)/(detector gain at reference VGA control voltage)

(Detector Attenuation (dB) versus VGA control voltage established by pre-flight calibration) Non-attenuated Waveform Amplitude (in counts) = Recorded Waveform Amplitude (in counts) * Waveform Amplitude Scale Factor

PWIDTH* Electronic Pulse Width (counts, not calibrated). Duration that the Channel 1 received energy exceeded the Channel 1 threshold.

AVERAGE* Software equivalent of a digitizer divider. The two channels (A & B) of the digitizer each sample at a MHz rate established by adjustable parameters (DIGI_CLOCK and DIGI_DIV). The two channels where then either recorded separately and stored in even and odd bin positions in the WAVEFORM array, or averaged together before storing as a single waveform bin value:

= 1 for internal, averaging implemented (almost always the case)

= 0 for external, no averaging

BIN_SIZE* Round-trip (i.e., two-way) travel time duration of digitizer bin (in nanoseconds). Time between samples for the digitizer. Speed of light = 299792458.0d-09 (m/nsec)

One-way BIN_SIZE (m) = BIN_SIZE (nsec) * (299792458.0d-09 / 2.) (m/nsec)

WAVEFORM* Array[150] of raw digitizer bin values (in byte counts)

STRUCTURE: SLA02.WAVGRP (SHOT CLASSIFICATION AND

WAVEFORM PROCESSING PARAMETERS GROUP, ONLY RTYP=15, 25)

** Structure FWAV, 5 tags, length=108

BL STRUCT -> BASLIN Array[1]

WF STRUCT -> WVFRM Array[1]

EN STRUCT -> ENVRN Array[1]

CL STRUCT -> CLASS Array[1]

GM STRUCT -> GMOD Array[1]

STRUCTURE:SLA02.WAVGRP.BL ( BASELINE PARAMETERS GROUP)

(digitizer noise characterization)

TAG NAME & DESCRIPTION

NPOINTS* Number of bins at the start of the waveform used to define the noise baseline.

MEAN* Mean of the noise baseline (in raw digitizer counts).

SIG* Standard deviation of the noise baseline (in raw digitizer counts).

STRUCTURE:SLA02.WAVGRP.WF (WAVEFORM PARAMETERS GROUP)

TAG NAME & DESCRIPTION

START* Position of the first bin in the waveform where the signal increases above MEAN + SIG

NPOINTS* Width of the signal (in bins). Defined as the number of bins from START to the last bin where the signal falls below the amplitude level of the START bin.

MAX* Maximum digitizer return signal (non-attenuated waveform amplitude counts)

WIDTH* Width (in nanoseconds) = NPOINTS * BIN_SIZE

AMPLITUDE* Maximum amplitude – noise baseline mean = MAX – MEAN (non-attenuated waveform amplitude counts)

(AMPLITUDE is zero referenced; baseline mean is subtracted to account for offset amplitude added to entire waveform after application of detector and digitizer scale factors)

AREA* Area under the waveform signal above the noise baseline mean from START to START + NPOINTS (non-attenuated waveform amplitude counts * nanoseconds)

STRUCTURE:SLA02.WAVGRP.WF (WAVEFORM PARAMETERS GROUP) (cont.)

TAG NAME DESCRIPTION

MMNT* Moments of the signal above the baseline mean from START to START + NPOINTS.

MEAN centroid of the distribution of return signal power (nsec), relative to START of signal above noise.

SIG 1 sigma deviation of the distribution (nsec).

SKEW skew of the distribution (unitless).

KURT kurtosis of the distribution (unitless).

NMAX* number of Gaussian peaks fitted to waveform between START and START + NPOINTS. (Based on identification of maxima from first and second derivatives and subsequent optimization of least-squares fitting of NMAX Gaussian distributions to signal above baseline mean.)

STRUCTURE:SLA02.WAVGRP.EN ( BOUNCE-POINT ENVIRONMENT PARAMETERS GROUP)

(SEE APPENDED NOTES FOR INFORMATION ON EXTERNAL DATA SETS)

TAG NAME DESCRIPTION

DEM* Elevation from Terrain Base 5 minute resolution Digital Elevation Model (in meters above Mean Sea Level,DEM = 0 for water) derived by bi-linear interpolation at the bounce point location using the four closest Terrain Base grid cells.

NDVI1* Normalized Difference Vegetation Index (NDVI, from Global Land Advanced Very High Resolution Radiometer (AVHRR) Pathfinder project. Values range from –1 to 1, interpolated from a global composite grid at the location of the SLA bounce point.

NDVI2* NDVI value from a 10-day composite corresponding to the closest available period to the STS-85 Mission (August11-20, 1997). (Not yet provided)

LANDCOVER* Global land cover classification from satellite data (ISLSCP).

SLOPE* Slope magnitude computed from DEM (in meters). (Not yet provided)

ROUGHNESS* Surface roughness (relief) from DEM (in meters). (Not yet provided)

STRUCTURE:SLA02.WAVGRP.CL (WAVEFORM CLASSIFICATION PARAMETERS GROUP)

TAG NAME & DESCRIPTION

RTYP* Return type

Ocean Returns (defined to be where DEM = 0.)

21 = No range over ocean

22 = Noise above range gate over ocean

23 = Noise above clouds (ORTHO_HT >10,000 m) over ocean

24 = Clouds or noise above ocean surface ( ORTHO_HT > 20 m)

25 = Surface return from ocean (ORTHO_HT within +/- 20 m)

26 = Noise below the ocean surface (ORTHO_HT < -20 m)

27 = Noise below the range gate over ocean

Land Returns (defined to be where DEM > 0.)

11 = No range over land

12 = Noise above range gate over land

13 = Noise above clouds (ORTHO_HT >10,000 m) over land

14 = Clouds or noise above land surface (ORTHO_HT-DEM > 500 m)

15 = Surface return from land (ABS(ORTHO_HT-DEM) <= 500 m)

16 = Noise below land surface (ORTHO_HT-DEM) < -500 m)

17 = Noise below the range gate over land

STYP* Saturation class (5 categories)

0 = no saturation

1 = near saturation

2 = linear saturation (slightly saturated waveform that can be treated as non-saturated waveform)

3 = non-linear saturation (type I) (deeply saturated)

4 = non-linear saturation (type II) (in fact not a saturation case, but a dip artifact in large peaks caused by stuck bit on one of the digitizer channels)

DTYP* Digitizer jitter class (4 categories) (Not yet provided)

RMS* Pulse spreading measured as the RMS roughness of the signal above the baseline mean from

ASPECT* A measure of pulse broadening = AMPLITUDE / WIDTH

LP_CENTROID* Distance from signal START to centroid of the last maximum derived from Gaussian fits (in meters, for one-way travel distance after multiplying by Speed of Light (m/nsec) / 2.) (equal to wv_centroid if only one maximum found)

WV_CENTROID* Distance from signal START to centroid of full waveform (in meters, for one-way travel distance after multiplying by Speed of Light (m/nsec) / 2.)

STRUCTURE: SLA02.WAVGRP

(SHOT CLASSIFICATION AND

WAVEFORM PROCESSING PARAMETERS GROUP) (cont.)

STRUCTURE:SLA02.WAVGRP.GM (GAUSSIAN FIT TO WAVEFORMS PARAMETERS GROUP)

(Gaussian fit of last maximum of multi-maxima waveform, or the one maximum of a single-maximum waveform)

TAG NAME & DESCRIPTION

CFFLAG* Flag indicating convergence status of least-squares Gaussian fitting routines model.

0 Convergence occurred before 40 iterations.

1 Failed to converge by 40th iteration; best fit results reported.

2 Shot not processed, due to several possible reasons:

1. Range = 0.
2. Maximum amplitude of raw waveform < 15 byte counts
3. Maximum amplitude of scaled waveform < 1000 non-attenuated waveform amplitude counts
4. No baseline found to define background noise
5. Number of bins in signal (NPOINTS) < 5 or > 100
6. More than 10 maxima found

G0* Amplitude of Gaussian fit to last maxima, in scaled units (non-attenuated waveform amplitude counts).

G1* Position of Gaussian fit to last maxima, as distance from START to center of last peak, in meters (based on 1-way BIN_SIZE). (same as LP_CENTROID, since only last peak parameters are stored)

G2* Width of Gaussian fit to last maxima, as 1 sigma variance, in meters (based on 1-way BIN_SIZE).

CHISQ* Chi-square value of least-squares Gaussian solution (square of the differences between the summation of the Gaussian fits to all maxima (NMAX) and the scaled waveform signal).

NITR* Number of iterations needed for convergence (Maximum number of iterations allowed = 40).

Notes:

Sources for Environmental Parameters provided:

These data sets can be retrieved from the Earth Resources Observations Systems (EROS) Data Center Distributed Active Archive Center (EDC DAAC).

URL: http://edcwww.cr.usgs.gov/landdaac

DEM Source Data:

National Geophysical Data Center TerrainBase, 5 minute Global DTM Version 1.0 TBASE.BIN.

Area Coverage: Worldwide (90N to 90S x 180W 180E). Bathymetry was set to zero in SLA data set, reporting only interpolated elevations at the bounce point locations over land.

URL: http://zenith.ngdc.noaa.gov/seg/fliers/se-1104.shtml

Land Cover data:

Global land cover classification from satellite data (ISLSCP).

URL: http://edcwww.cr.usgs.gov/landdaac/glcc/glcc.html

NDVI source data characteristics:

URL: http://edcwww.cr.usgs.gov/landdaac/1KM/data_access.html

The original data set included values between 10 and 210, shifted and scaled from real values between –1 and 1). Values from 0 to 9 had been reserved for special masks (water, Goode’s interrupted area, no data, etc). To accomplish this, a shift value is added to each pixel prior to scaling.

Equations for scaling and un-scaling values:

scaled = (actual + shift) * scale + offset

actual = (scaled - offset) / scale - shift

Masks used in shifted and scaled source:

0 = Missing Data Over Land

1 = Ocean

2 = Goode’s Interrupted Area

3 = Solar Zenith angle greater than 80 degrees

The shifted and scaled source file values were converted to NDVI values using:

scale = 100; offset = 10; shift = 1

The source file was first projected from the Goode’s projection to latitude and longitude and then sampled by bi-linear interpolation at the SLA bounce point location. During the interpolation:

If one or two of the four cells used for interpolation had one of the mask values, the NDVI value for the

point was calculated as the average between the NDVI values from the valid cells.

If three of the cells corresponded to the same mask value, then the NDVI was set to that

mask value. Otherwise, the value of -79.999 was returned.

After interpolating, masks values were set to:

-99.999 = no data over land

-9.999 = ocean

-69.999 = Goode's projection interrupted area

-59.999 = solar zenith >80

-79.999 = point not averaged nor interpolated in interpolation routine

Last Modified: 02/08/99

Claudia C. Carabajal (claudia@stokes.gsfc.nasa.gov)