# Presentation: 410897

## Section 5

***Advanced Land Imager***

***. . . ******Donald E. Lencioni***
*ALI Instrument Scientist *
*MIT Lincoln Laboratory*
***. . . ******Constantine J. Digenis***
*ALI Program Manager *
*MIT Lincoln Laboratory *

## ALI Overview 
Design and performance
Pre-launch Calibration and Characterization
Application to future Landsat instruments ---technology transfer
On-orbit performance assessment
Summary

***ALI Overview ***
***Design and performance***
***Pre-launch Calibration and Characterization***
***Application to future Landsat instruments ---technology transfer***
***On-orbit performance assessment***
***Summary***

***Topics of Discussion***

## EO-1 Advanced Land Imager Overview

***EO-1 Advanced Land Imager Overview***

***Primary instrument on the first Earth Observing Mission (EO-1) of NASA’s New Millennium Program (NMP) ***
***Objectives are to flight validate key technologies***
***Data continuity, advanced capability and cost reduction for future Landsat instruments***
***Innovative approaches to future land imaging***
***The ALI instrument was designed and developed by MIT Lincoln Laboratory with NMP instrument team members***
***Raytheon SBRS for the focal plane system***
***SSG Inc. for the optical system***

## Driving Requirements

***Driving Requirements***

***Instrument architecture developed from technologies represented on the NMP IPDT***
***Flight validation of technologies required to significantly reduce the risk for future missions ***
***Flight data must be amenable to science validation ***
***Measurement requirements were developed***
***From the bottom up by the IPDT***
***In collaboration with the earth science community***
***Design must be scaleable to a full-up instrument***

## Advanced Land Imager (ALI)

## ALI Optical Design Form

**Notes:**
Design form chosen for the ALI. This is a three mirror anastigmat (TMA) or Cooke Triplet, named after Lacy Cooke the inventor of this design.  This design supports a large field of view in one dimension and a relatively small one in the other. This is ideal for a bush-broom sensor design with a large cross-track FOV. 

## Main Focal Plane Assembly

**Notes:**
Although the optical system supports a 15° wide FOV, only 3° was populated with detector arrays as illustrated here. The multispectral panchromatic (MS/Pan) array has 7 spectral bands in the visible and near infrared (VNIR), and 3 in the short wave infrared (SWIR). 
Four sensor chip assembles (SCA’s) populate the 3° cross-track segment of the focal plane.  Each MS band on each SCA contains 320 detectors in the cross-track direction, while each pan band contains 960 detectors.  The total cross-track coverage from the single MS/Pan module is 37 km.
The MS/Pan arrays use Silicon-diode VNIR detectors fabricated on the Silicon substrate of a Readout Integrated Circuit (ROIC).  The SWIR detectors are Mercury-Cadmium-Telluride (HgCdTe) photo-diodes that are Indium bump-bonded onto the ROIC that services the VNIR detectors.  These SWIR detectors promise high performance over the 0.9 to 2.5 mm wavelength region at temperatures that can be reached by passive or thermoelectric cooling.  The nominal focal plane temperature is 220K and is maintained by the use of a radiator and heater controls.

## ALI Spectral Response Functions

**Notes:**
There were two primary methods used to determine the normalized spectral response functions in our calibration plan. The first relies on combining the individual component measurements, i.e., the spectral reflectance of the four mirrors, the transmissions of the filters, and the detector responses. The product of these terms when normalized to the peak is expected to give an accurate estimate of the system response. Note that errors in this function are of second order since the magnitude of the transmission is carried in the response coefficients CN . Nevertheless measurements were also made at the system level to to detect effects such as vacuum induced changes, contamination, etc. The two approaches have thus far been compared only in the VNIR bands and have indicated excellent agreement. An example is given in here for Band 3. 

## EO-1 ALI MS/PAN Spectral and Spatial Coverage

**Notes:**
Summary of the ALI spectral bands, the detector materials for each band, the ground sample distances (GSD), and the number of detectors in each band.

## MS/PAN Flight Module

***MS/PAN Flight Module***

**Notes:**
This is a photograph of the actual MS/PAN flight module.

## Slide 11

**Notes:**
This is a photograph of the actual flight focal plane array assembly.

## Partially Assembled Flight ALI

_***Telescope features***_
***12.5 cm entrance pupil***
***15° x 1.26° field-of-view***
***Telecentric,  f/7.5 design***
***Unobscured,  reflective optics***
***Silicon carbide mirrors***
***Wavefront error = 0.11 ************RMS @ 633 nm***

**Notes:**
Flight ALI mounted on the aluminum flight pallet prior to the housing installation. Note the external calibration source mounted on the left side of the metering truss.

## Installation of ALI into Thermal Vacuum Chamber

**Notes:**
The completely assembled ALI is shown here being installed into the thermal vacuum chamber for testing. The approximately 0.9m (X) x 0.9m (Y) x 0.7m (Z) size instrument sits on an aluminum pallet that attaches to the spacecraft.  In orbit the instrument is wrapped in Multi-Layer Insulation (MLI). The thermal radiators for the Focal Plane and the Focal Plane Electronics are outside the MLI wrap.  The telescope is under the MLI surrounded by a thin (~1mm) aluminum housing that supports an aperture cover. The ALI Control Electronics and the Focal Plane Electronics (FPE) packages are supported on the pallet outside the telescope housing. 

## Solar Calibration

**Notes:**
The on-orbit absolute calibration relies primarily on solar calibration, which is illustrated in this figure. For solar calibration there is a motor-driven aperture selector in the aperture cover assembly itself.  The aperture selector moves an opaque slide over a row of small to increasingly larger slit openings and then reverses the slide motion to block all light.  Just prior to solar calibration, a Spectralon diffuser plate is swung over the secondary mirror by a motor-driven mechanism.  The diffuser reflectively scatters the sunlight that would otherwise impinge on the secondary. During solar calibration the reflectively scattered sunlight exposes the FPA to an irradiance that is equivalent to earth-reflected sunlight for an earth albedo ranging from 0 to 100%. 

## ALI Calibration Matrix

## Imaging Test Optics

**Notes:**
Schematic of the Schmidt sphere imaging collimator which shows the translation stages located at the focus. These are used to move scenes across the ALI that replicate the data collection of an Earth scene from orbit. The actual optical setup is also shown. 

## Focus Test

**Notes:**
The integration of the ALI focal plane system with the telescope required determining the proper thickness for the shim which would place the FPA at the best-focus plane of the telescope. This was accomplished with the imaging collimator  by making successive knife-edge scans, with the plane of the knife-edge displaced by various distances from the true collimator focus position. For each scan, a figure-of-merit, such as the full width at half maximum of the detector line spread function normalized to the detector width,. was calculated, indicating the relative quality of the focus The figures of merit were plotted, and the position of the knife-edge was found which gave the best focus. The distance of that position from the true collimator focus, when multiplied by the square of the ratio of focal lengths (ALI telescope to collimator), was the estimated focus error in the ALI. The FPA was then removed, the shim was corrected, and the process was repeated. In this case, only one cycle of shim adjustment was made. This process is depicted in this figure.

## MTF Performance

**Notes:**
To measure the system MTF’s of the ALI, knife-edge scans were made across representative pixels of each band and each sensor chip assembly (SCA), in both cross-track and in-track directions. These were generated by scanning the knife edge at the focus of the imaging collimator and projecting the beam into the ALI which was in the thermal vacuum chamber. The detected signals, when normalized to a response range of zero (black) to one (white), represent the edge-spread function (ESF) of each pixel. The derivative of the ESF is the line-spread function (LSF). The Fourier transform of the detector channel’s LSF provides the MTF’s. An example of this process is given in this figure.

## Image Reconstruction and Calibration MS Band 1

## ALI Dynamic Range and Linearity

## ALI SNR Performance

***ALI SNR Performance***

**Notes:**
Perhaps the most dramatic performance aspect of the ALI is the high SNR that is achieved with such a small optical aperture (12.5 cm). This is illustrated in here which summarizes the average SNR of all the bands for a 5% earth surface reflectance. These results are compared  to the SNR of the ETM+. 

## Growth Path to Advanced Instrument

***Growth Path to Advanced Instrument***

**Notes:**
One key element of the NMP technology validation for the ALI is the demonstration of scalability to a full up Landsat instrument. Several design features and tests have accomplished this result. The FPA was designed in a modular fashion so that the full 150  coverage could be achieved by simply replicating the ALI module four more times. The data rate increases by a factor of 5 while it is estimated that the electrical power of the FPA would increase about a factor of 3.  There would be no physical changes in the instrument design to accommodate this upgrade. Moreover, the optical subsystem performance was verified over the full 150 field of view. The placement of the populated detector module on the outer 30 of the available field was done deliberately to validate the most stressing portion of the FOV. This is shown above.

## Land Imaging Instrument Comparison

**296268-7P**

**Notes:**
This figure shows a comparison of the ETM+ and an ALI-based future Landsat instrument. An ALI with an fully populated FPA would exhibit about one-fourth the mass, one-fifth the power, and about one-third the volume compared to the ETM+ of Landsat 7. These along with the improved SNR make the EO-1 ALI  design and technologies very attractive for use in future missions.

## ALI Technology Transfer

***ALI Technology Transfer***

***Objectives***
***Reduce cost and improve data quality for the LDCM ***
***Exploit NASA’s investment in the ALI technologies ***
***Utilize Lincoln Laboratory’s unique ALI expertise***
***Methods ***
***Publications, reports, and documentation***
***NASA-sponsored  workshops at Lincoln Laboratory***
***Technical support of an industry/government sensor development ***
***Characterization and calibration of sensors at Lincoln Laboratory ***
***Sensor integration and test by Lincoln Laboratory ***
***Funding for MIT/Lincoln Laboratory (an FFRDC) ***
***Directly from NASA or other government agency***
***Cooperative Research and Development Agreement with industry developer ***

## Summary

***Summary***

***The Advanced Land Imager is the primary instrument on the first Earth Observing Mission (EO-1) of NASA’s New Millennium Program (NMP) ***
***The ALI has undergone extensive pre-launch calibration and characterization and has demonstrated excellent performance***
***The EO-1 mission is now in progress and should successfully flight-validate the NMP technologies ***
***These technologies provide a path for lower cost, higher performance, future Landsat instruments***
***MIT Lincoln Laboratory is interested in helping NASA transfer the ALI technology for application to future Landsat missions***

**Notes:**
The EO-1 Advanced Land Imager has undergone extensive pre-launch characterization and calibration. Although data analysis and performance assessments are still in progress, preliminary results indicate superior performance in resolution, image quality, SNR, dynamic range, radiometric accuracy, and repeatability. This performance has been achieved in a sensor of  considerably smaller size, lower weight, and requiring less power then previous instruments with similar Earth observing objectives. The EO-1 mission should successfully flight-validate the New Millennium Program technology and science objectives. It also provides a path for a lower cost, higher performance, Landsat follow-on. 

## On-Orbit Performance Assessment

***On-Orbit Performance Assessment***

***Preliminary flight data and status***
***On-orbit performance assessment plan***
***Summary***

## ALI Performance in Space

***ALI Performance in Space***

***ALI was turned on on November 25, 2000 (Day 5)***
***Launch latches were released and a series of comprehensive tests were conducted showing nominal instrument performance ***
***The temperature control has been excellent***
***Obtained four earth scenes with the spacecraft pointing to nadir, i.e., the active part of ALI covering a swath 55 to 92 km east of the S/C ground track***
***Alaska, north-east of Anchorage***
***East Antarctica***
***Marshall Islands***
***North-central Australia***

## Mission Operations

***Mission****** ******Operations***

***The first earth scene with all instruments operating simultaneously was obtained on December 1, 2000***
***On December 15, 2000, EO-1 achieved its intended position, 1 minute behind Landsat 7 ***
***On December 21, 2000, EO-1 began to point towards the desired target within the Landsat swath.  Until then, most of the recorded scenes represented targets of opportunity with the S/C in a nadir pointing mode***
***Comparison of ALI and Landsat scenes has not yet begun ***
***The number of scenes per day has gradually increased from two to six.  Eight is the planned maximum in the first four months.***
***Four scenes per day will be acquired in the remainder of the first year***
***No firm plans yet for the remainder of life (EO-1 has 5 years worth of consumables)***

## Focal Plane Contamination

***Focal Plane Contamination***

***Ground testing had revealed fine droplets forming on the cold focal plane after several days at –53 C.  They boil off between  –20 C and –10 C ***
***ALI is equipped with enough heaters to raise the focal plane temperature to –3 C which has been effective in evaporating the unknown contaminant***
***Bake-outs on-orbit were planned every two weeks***
***In space, it was noted that the contaminant accumulation is more severe and occurs faster than on the ground.  The bake-out is still effective in boiling off the contaminant(s).***
***Bake-outs will be conducted weekly and the performance will continue to be monitored closely***

## First ALI Image: Sutton, AK (2000:330, MS 3-2-1)

## First ALI Image: Sutton, AK  (2000:330, Pan zoom)

## Washington, DC(2000:356, MS 4-3-2)

## Washington, DC(2000:336, Pan zoom)

## Delaware Coast(2000:338, MS 4-3-2)

## Oahu,HI(2000:354, MS 3-2-1)

## Focal Plane Functional Tests

***Focal Plane Functional Tests***

***Zero signal noise characteristics***
***Internal lamp illumination***
***Responsivity***
***Linearity***
***Stability***
***Contamination assessment***
***On-orbit sensitivity to FPA and optics temperature ***
***Evaluation of dead and under performing pixels***
***Focal plane decontamination ***

## ALI Technology Validation: Spatial Tests

***ALI Technology Validation: Spatial Tests***

***Functional test of end to end imaging ***
***Focus***
***Point spread***
***Edge spread***
***Line spread***
***MTF***
***Relative pixel line of sight***
***Band to band image displacement accuracy***
***Image artifacts ***

## ALI Technology Validation: Radiometric Tests

***ALI Technology Validation: Radiometric Tests***

***Pixel to pixel calibration (flat field)***
***Calibration stability***
***Absolute calibration***
***In-band***
***Band to band***
***Dynamic range***
***Saturation***
***Noise***
***Sensitivity (SNR)***
***Solar calibration***
***Lunar calibration scan***
***Calibration corrections for leaky pixels***
***Linearity***
***Dynamic range***
***Stray light effects***
***Spatial***
***Radiometric***

## Generic Data Collection Events (DCE)

***Generic Data Collection Events (DCE)***

***A.******	******Large flat metropolitan area with shore line***
***High contrast edge lines and points***
***Well known locations of key features***
***B.******	******Extended high albedo source with small dark regions***
***Clouds over ocean***
***C.******	******Steep topography***
***D.******	******Long bridges***
***F.******	******Large area with uniform known radiance (5-50% albedo)***
***G.******	******Adjacent regions with sharp boundaries and having different, uniform, but not necessarily known radiance levels***
***H.******	******Large area with uniform but unknown radiance***
***J.******	******MODIS calibration sites***
***K.******	******Landsat 7 geometric calibration sites***
***L.******	******Sun***
***M.******	******Moon ***
***N.******	******Closed Cover (dark current)***
***O.******	******Night view of brightly lit metropolitan area***
***S.******	******Ground truth and under-flight targets***
***T.******	******Long duration target***
***U.******	******Angular dependence demonstration***

## Summary

***Summary***

***The performance of the Advanced Land Imager in space has been nominal.***
***The radiometric calibration coefficients will be revised based the imaging of known ground scenes and the solar calibration.***
***An improved algorithm has been developed to deal with the two leaky pixels.***
***Weekly bake-outs of the focal plane will be conducted to boil off the accumulating contaminants.***
***The required data base is been collected and will be followed by in-depth analysis of all aspects of instrument performance.***