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Radiometric Requirements

Radiometric Requirements. Hartmut Boesch University of Leicester. Study Overview. Included radiometric uncertainties: Multiplicative radiometric errors Additive radiometric errors (Zero-level offset) Non-linearity Scenarios Nadir: vegetation Glint: windspeed between 1 and 10 m/s

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Radiometric Requirements

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  1. Radiometric Requirements Hartmut Boesch University of Leicester

  2. Study Overview • Included radiometric uncertainties: • Multiplicative radiometric errors • Additive radiometric errors (Zero-level offset) • Non-linearity • Scenarios • Nadir: vegetation • Glint: windspeed between 1 and 10 m/s • SZA: 5 - 70o • Aerosol/cirrus-free (AOD = 0.03, COD = 0.03) • Biases have been inferred with gain-matrix approach (linear error analysis)

  3. Multiplicative Radiometric Errors - Nadir Assumption: 1% error in multiplicative gain XCO2 Bias All 3 Bands NIR SWIR-1 SWIR-2 XCH4 Bias • Errors in XCO2 and XCH4 typically < 0.1% • Strong error compensation in the case of gain errors in all 3 band

  4. Multiplicative Radiometric Errors - Glint Assumption: 1% error in multiplicative gain XCO2 Bias XCH4 Bias • Errors are much larger than for nadir and can be a couple of % • Again, error compensation in the case of gain errors in all 3 band • Including additional continuum scaling should reduce these errors

  5. Additive radiometric errors - Nadir • Assumption: Zero-level offset error • NIR: 2.1 x 109 ph/s/nm/cm2/sr • SWIR-1: 2.2 x 109ph/s/nm/cm2/sr • SWIR-2: 3.2 x 108 ph/s/nm/cm2/sr XCO2 Bias NIR SWIR-1 SWIR-2 XCH4 Bias • Errors in XCO2 and XCH4 typically < 0.15% • Largest errors are found for SWIR-1

  6. Additive radiometric errors - Glint XCO2 Bias XCH4 Bias • Similar or slightly (for CH4) larger error than for nadir • Largest errors are found for SWIR-1 and SWIR-2 (for XCO2)

  7. Non-Linearity Correction- Nadir Assumption: Pixels within a band with lowest intensity have calibration error of 0.05% while pixels with highest intensity have no calibration error. XCO2 Bias NIR SWIR-1 SWIR-2 XCH4 Bias • Errors in XCO2 and XCH4 typically < 0.1% • Glint errors are of similar magnitude

  8. Summary • Radiometric calibration uncertainties for multiplicative gain, additive offset and non-linearity has been investigated • Within the assumed uncertainties, XCO2 and XCH4 errors due to radiometric calibration uncertainties are small for additive offset and non-linearity • Errors due to multiplicative gain uncertainties for nadir mode are small but larger errors (>1%) are found for sunglint mode for uncertainties of single bands • Inclusion of continuum scaling or Lambertian offset in the glint retrieval might lead to a reduction of these larger errors for multiplicative gain

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