ATLID L1 Validation
Discussion

What is in the L1 product ?
Calibrated cross-talk corrected ATBS
andDecomposed error estimatesIntermediate products
Cross-talk coefficients usedRaw Signals
Etc..
Data is NetCDF4/HDF5 ! Following
similar conventions used in L2 data !

What does ESA expect from the Cal/Val teams ?
• Data submission to Cal/Val data base.
• Original terrestrial lidar observations ?
• Final products e.g. filtered terrestrial ATLID(-like) L1 products derived fromterrestrial measurements ?
• Both ?

• Attendance of work-shops.
• Publishing/presentation of results ?

How do we validate L1 (I) ?
• What measurements and conditions to prioritize ?
• Measurements at 355 nm.
• Measurements covering the stratospheric aerosol layer ?
• Coordinated under flights with aircraft based lidars.
• Homogeneous aerosol fields• Ground-based longer-term observations.
• Statistical approaches.
• Filtering for homogeneous conditions.
• Homogeneous Aerosol field.
• “Homogeneous Cirrus” (esp. depol validation) cases desirable.

How do we validate L1 (II) ?
• Validation of Rayleigh Calibration• ATLID L1 will come with T and P (via ECMWF) fields. Are these good enough ? Would the use of
local Radiosondes (not assimilated by the ECMWF) be useful?

• Common, lidar specific standards for Cal/Val purposes, e.g. well calibrated depolarization
measurements including errors.
• Who will draft the standards/conventions and how will this process proceed ?

• Can we use data not at 355nm ?
• ATBs can not be directly compared between ground and space-based systems.
Ground L1 è L2 to Space L1 simulations will be necessary.

• Simple –vs- complex simulations ?
• Will enough information on ATLID parameters be available to the validation community for themto conduct advanced simulations ?

For CALIPSO: The approach of using Ground-based L2 products to simulate space-based L1 was successfullyimplemented. e.g.

For UV systems the need is even more obvious !

Example at 355 nm
PollyXT_TROPOS; Leipzig, Germany,
27 March 2020. 1830-1930 UTC

Height [km]16Pl ( z ) =particle
molecular

128400480 50 100 150 200 250-1-1Backscatter coeff. [Mm sr ] Extinction coeff. [Mm -1]l

C O ( z)z2ìïüïllléë b paùé lùr ( z ) +b mol ( z ) û exp í -2 ò ëa par ( r ) + a mol ( r ) û dr ý
îï z1
þï
z2

16
from ground: z1=0 km
from space: z1= 20 km

Height [km]

2020l
sys

from groundfrom space

128

With measured backscatterand extinction profiles from 4
ground one can calculate
the attenuated backscatter 0
from space!
04
8
Attenuated Backscatter coeff.
[Mm-1 sr-1]

Validation of the attenuatedbackscatter
Some thoughts

The attenuated backscatter coefficientz2
éùlllllbattn = bmol + bpar exp ê -2 ò a mol + a par dz úêë z1
úû()• Is not the same from space and from ground• attenuation can not be neglected at 355 nm• Is a EarthCARE L1 product

The lidar equation
Pl ( z ) =lCsys
Ol ( z)

P ( z) =lz2lsysz2
ìüï
ïllll
éë b par ( z ) +b mol ( z ) ùû exp í-2 ò éëa par ( r ) + a mol ( r ) ùû dr ýîï z1þïlC O ( z)z2lb attn

O=1

l
2Pzz()
lb attn =(Level 1)
lCsys

The attenuated backscatter coefficientz2éùlllllbattn = bmol + bpar exp ê -2 ò a mol + a par dz úêë z1
úû()• Is not the same from space and from ground• attenuation can not be neglected at 355 nm• Is a EarthCARE L1 product

The lidar equation
Pl ( z ) =lCsys
Ol ( z)

P ( z) =lz2
lsysz2ìüïïlllléë b par ( z ) +b mol ( z ) ùû exp í-2 ò éëa par ( r ) + a mol ( r ) ùû dr ý
îï z1
þïl

C O ( z)z2lb attnO=1l2Pzz()
lb attn =(Level 1)
lCsys

Molecular influence and attenuation
Attenuated backscatter from ground at 3 wavelengths

355nm

P ( z) zlb attn =lCsysl

21064 nm

532nm

1064nmll@1064 nmb attn» b parBut for shorter wavelengths
attenuation need to be taken intoaccountll@355 nmb attn¹ b parLevel 1 –2 data comparisons
Methodology developed for retrieving
CALIPSO-like Level1 data from groundbased elastic/Raman techniqueMona etLevel 1

al., 2009 ACP

Systematic comparison: absence of biases
and main problems in CALIPSO detectedsignals
Pappalardo et al., 2010 JGRCALIPSO Level 2 data generally perform well both in terms ofoptical profiles and layer identification.
Level 2
Some critical points:§cloud-aerosol discrimination§lidar ratio assumptions§multiple scattering for aerosol below cirrus and large dust
particles
Courtesy Lucia Mona