STAR - Global Vegetation Health Products : AVHRR calibration
This page describes the AVHRR calibration parameters used by VHP project.
- Pre-launch calibration file
- Post-launch calibration file
- Active Calibration for VHP project
- Table of Post-Lunch Calibration Slope
1: Pre-launch calibration file
File name:
AVHRR_calibration_prelaunch.txtDescription:
This is a static file, includes launch date and pre-luanch calibraion for each satellite: NOAA 7 to 19, M1 and M2.2: Post-luanch calibraion file
File name:
AVHRR_calibration_postlaunch.txtDescription:
This file is updated monthly, includes post-luanch calibraion for each satellite: NOAA 16 to 19, M1 and M2. We use the the following varibales to calculate the post-launch calibration (S, i.e. ratio of R/R_prelauch).
- "reflectance constant" and "degredation rate" are read from post-launch calibration file.
- "days Since Launch" was calulated from current date and the date when satellite was launched
- "reference reflectance" are pre-defined, static numbers for band 1 and 2.
float Reference_Reflectance_Of_CH1 = 37.80; float Reference_Reflectance_Of_CH2 = 42.60; a1= (CH1.reflectance_constant + CH1.degradation_rate * daysSinceLaunch); a2= (CH2.reflectance_constant + CH2.degradation_rate * daysSinceLaunch); S1 = Reference_Reflectance_Of_CH1 /a1; S2 = Reference_Reflectance_Of_CH2 /a2;
exmaple:
#post-launch calibration with the most recent update. #data source= https://www.star.nesdis.noaa.gov/smcd/spb/fwu/homepage/AVHRR/Op_Cal_AVHRR/Op_Cal_AVHRR.html #Sat CH Update Data Center Constant Deg. Rate sin cos Amp. Angle Mean Ratio Slope_lo Int_lo Slope_hi Int_hi NL CH1: 09/24/2013 09/07/2007 10/26/2013 38.7391 -0.1277% -0.4390 -0.4089 0.5999 42.96 32.63 1.1584 0.06066 -2.339 0.1771 -60.18 NL CH2: 09/24/2013 09/07/2007 10/26/2013 40.5308 -0.1742% -0.1953 -1.3403 1.3544 81.71 32.20 1.3231 0.06786 -2.563 0.1999 -68.61 NM CH1: 09/28/2010 09/24/2010 10/26/2010 39.5504 -0.0995% -0.2193 0.4581 0.5079 -64.42 36.52 1.0351 0.05737 -2.296 0.1684 -57.94 NM CH2: 09/28/2010 09/24/2010 10/26/2010 37.0158 -0.1198% -1.0015 0.0726 1.0041 -4.15 33.37 1.2768 0.06944 -2.726 0.2067 -71.57 NM CH3: 09/28/2010 09/24/2010 10/26/2010 59.2315 -0.2189% 0.0068 1.3414 1.3414 89.71 52.56 1.2728 0.03373 -1.422 0.2364 -103.22 NN CH1: 09/24/2013 09/17/2013 10/26/2013 39.9964 -0.1373% 0.0430 0.6667 0.6681 86.31 35.77 1.0569 0.05707 -2.250 0.1702 -58.52 NN CH2: 09/24/2013 09/17/2013 10/26/2013 38.7937 -0.1547% -0.9087 0.7444 1.1746 -39.32 34.03 1.2520 0.06623 -2.609 0.1987 -69.24 NP CH1: 09/24/2013 09/23/2013 10/26/2013 41.0745 -0.0599% 0.6506 -0.1431 0.6661 -12.40 40.04 0.9440 0.05201 -2.022 0.1534 -52.74 NP CH2: 09/24/2013 09/23/2013 10/26/2013 41.9109 -0.1331% 1.1734 0.6702 1.3513 29.73 39.62 1.0753 0.05902 -2.289 0.1758 -60.70 NP CH3: 09/24/2013 09/23/2013 10/26/2013 36.7549 39.2989%-13.6567 23.176126.9005 -59.49 714.27 0.0937 0.00255 -0.102 0.0176 -7.63 M2 CH1: 09/24/2013 09/17/2013 10/26/2013 39.0906 -0.0924% -0.1924 -0.4161 0.4584 65.18 36.72 1.0294 0.05529 -2.236 0.1634 -56.39 M2 CH2: 09/24/2013 09/17/2013 10/26/2013 38.4566 -0.1394% 0.4001 -1.1163 1.1858 -70.28 34.88 1.2213 0.06658 -2.646 0.1977 -68.28 M2 CH3: 09/24/2013 09/17/2013 10/26/2013 58.0146 -0.1815% -1.0043 -0.6548 1.1989 33.10 53.36 1.2538 0.03316 -1.363 0.2303 -100.31 M1 CH1: 11/23/2012 11/23/2012 11/23/2012 0.0514560 -2.0255039 0.1523520 -52.5609589 M1 CH2: 11/23/2012 11/23/2012 11/23/2012 0.0563066 -2.2743661 0.1658762 -57.4006653The post-luanch calibraions for M1 is for in "intitial stage". Thus, no degradation rate is provided.
3. Active Calibration for VHP project
File name:
avhrr_cali_allyears_active.txtexample:
[Active Calibration] 1981 week=35 sat=NC CH1: 0.11075, -3.98689, 0.00000, 0.00000, 1024.00000 CH2: 0.11784, -4.36022, 0.00000, 0.00000, 1024.00000 AdjustmentForNDVI=1.050000
format:
[Active Calibration] year week=xx sat=xx CH1: slope_lo,Int_lo, Slope_hi,Int_hi, breakpoint, CH2, slope_lo,Int_lo, Slope_hi,Int_hi, breakpoint AdjustmentForNDVI=xxxx
Description:
(1) Active calibration is that we used in our project; with both pre-launch and post_launch calibration applied.
(2) slop and intercept is the active calibration which will be applied to channel's count value (ch_count):
postcalibrated_reflectance = slope * ch_count +intercept;
if(ch_count < breakpoint) use parameters for low gain, otherwise use parameters for high gain.
(3) AdjustmentForNDVI is the amount to adjust on NDVI:
adjusted_NDVI= AdjustmentForNDVI * NDVI
4. Table of Post-Lunch Calibration Slope
File name:
avhrr_cali_allyears_slope.txtexample:
[Note on Calibration] 1981 week=35 (jday=241): NC, daysSinceLaunch= 67; S1/S1_day1= 1.006688, S2/S2_day1= 1.007951; S1= 0.110747 S2= 0.117844; D1= 36.0, D2= 37.0
Description:
NC: satellite ID for NOAA-7
jday: day of year
daysSinceLaunch: number of days since this satellite was launched
S1, S2: post-launch calibration for band 1 and 2 for the give day
D1, D2: dark count for band 1 and 2
S1_day1.S1/day2, post-launch calibration for band 1 and 2 for the day when this satellite was launched.
For NOAA 7 to 14:
Reflectance = S1 * ( ch_count - D1)
which is eqivalent to :
m_caliCH1.low_gain_slope = S1;
m_caliCH1.low_gain_intercept = -S1 * D1;
Reflectance = m_caliCH1.low_gain_slope * ch_count + m_caliCH1.low_gain_intercept
Since it is single slope, high gain section will not be used.
For NOAA 15 to 19:
first, load slope and intercept (for low and high gain) and launch date from prelauched calibration file.
see AVHRR_calibration_prelaunch.txt for detail.
then , apply the post-launch calibration coefficients, S1 and S2:
m_caliCH1.low_gain_slope *= S1;
m_caliCH1.low_gain_intercept *= S1;
m_caliCH1.high_gain_slope *= S1;
m_caliCH1.high_gain_intercept *= S1;
Reflectance = m_caliCH1.low_gain_slope * ch_count + m_caliCH1.low_gain_intercept